SQL Interview questions

How would you find out the total number of rows in a table?
Use SELECT COUNT(*) ... in query
How do you eliminate duplicate values in SELECT ?
Use SELECT DISTINCT ... in SQL query
How you insert records into a table
Using SQL INSERT statement
How do you delete record from a table ?
Using DELETE statementExample : DELETE FROM EMP
How do you select a row using indexes?
Specify the indexed columns in the WHERE clause of query.
How do you find the maximum value in a column?
Use SELECT MAX(...) .. in query
How do you retrieve the first 5 characters of FIRSTNAME column of table EMP ?
SELECT SUBSTR(FIRSTNAME,1,5) FROM EMP
My SQL statement SELECT AVG(SALARY) FROM EMP yields inaccurate results. Why?
Because SALARY is not declared to have NULLs and the employees for whom the
salary is not known are also counted.
How do you concatenate the FIRSTNAME and LASTNAME from EMP table to give a complete name?
SELECT FIRSTNAME ‘ ‘ LASTNAME FROM EMP
What is UNION,UNION ALL in SQL?
UNION : eliminates duplicatesUNION ALL: retains duplicatesBoth these are used to combine the results of different SELECT statements.
Suppose I have five SQL SELECT statements connected by UNION/UNION ALL, how many timesshould I specify UNION to eliminate the duplicate rows?
Once.
In the WHERE clause what is BETWEEN and IN?
BETWEEN supplies a range of values while IN supplies a list of values.
Is BETWEEN inclusive of the range values specified?
Yes.
What is 'LIKE' used for in WHERE clause? What are the wildcard characters?
LIKE is used for partial string matches. ‘%’ ( for a string of any character ) and ‘_’ (for any single character ) are the two wild card characters.
When do you use a LIKE statement?
To do partial search e.g. to search employee by name, you need not specify the complete name; using LIKE, you can search for partial string matches. Example SQL : SELECT EMPNO FROM EMP WHERE EMPNAME LIKE 'RAMESH%' % is used to represent remaining all characters in the name.This query fetches all records contains RAMESH in six characters.
What do you accomplish by GROUP BY ... HAVING clause?
GROUP BY partitions the selected rows on the distinct values of the column on which you group by. HAVING selects GROUPs which match the criteria specified
Consider the employee table with column PROJECT nullable. How can you get a listof employees who are not assigned to any project?
SQL : SELECT EMPNO FROM EMP WHERE PROJECT IS null;
What are the large objects supported by oracle and db2?
Blob , Clob ( Binary Large Objects, Character Large Objects)
What's the difference between a primary key and a unique key?
Primary key wont allow nulls, unique key allow nulls.Both Primary key and Unique key enforce the uniqueness of the column on which they are defined.
What is a join and explain different types of joins?
INNER JOINOUTER JOINLEFT OUTER JOINRIGHT OUTER JOINFULL OUTER JOININNER JOIN
What is a self join?
Joining two instances of a same table. Sample SQL : SELECT A.EMPNAME , B.EMPNAME FROM EMP A, EMP B WHERE A.MGRID = B.EMPID
What is a transaction and ACID?
Transaction - A transaction is a logicl unint of work. All steps must be commited or rolled back.ACID - Atomicity, Consistency, Isolation and Duralbility, these are properties of a transaction.
Materialized Query Tables in db2 ( This feature might not be available in oracle) ?
Materialized Query Tables or MQTs are also known as automatic summary tables. A materialized query table (MQT) is a table whose definition is based upon the result of a query. The data that is contained in an MQT is derived from one or more tables on which the materialized query table definition is based. MQT improve the query performance. Sample SQL to creat MQT. CREATE TABLE CUSTOMER_ORDER AS (SELECT SUM(AMOUNT) AS TOTAL_SUM, TRANS_DT, STATUS FROM DB2INST2.CUSTOMER_ORDER WHERE TRANS_DT BETWEEN '1/1/2001' AND '12/31/2001' GROUP BY TRANS_DT, STATUS) DATA INITIALLY DEFERRED REFRESH DEFERRED; 1. Q. What does SQL stand for? A. Structured Query Language 2. Q. How do you select all records from the table? A. Select * from table_name; 3. Q. What is a join? A. Join is a process of retrieve pieces of data from different sets (tables) and returns them to the user or program as one “joined” collection of data. 4. Q. What kinds of joins do you know? Give examples. A. We have self join, outer joint (LEFT, RIGHT), , cross-join ( Cartesian product n*m rows returned)Exp:outer jointSELECT Employee.Name, Department. DeptName FROM Employee, DepartmentWHERE Employee.Employee_ID = Department.Employee_ID; cross-joinSELECT * FROM table1, table2; self joinSELECT e1.name ’ ‘ e2.ename FROM emp e1, emp e2 WHERE e1. emp_no = e2.emp_no; The following summarizes the result of the join operations: · The result of T1 INNER JOIN T2 consists of their paired rows where thejoin-condition is true.· The result of T1 LEFT OUTER JOIN T2 consists of their paired rows wherethe join-condition is true and, for each unpaired row of T1, theconcatenation of that row with the null row of T2. All columns derivedfrom T2 allow null values.· The result of T1 RIGHT OUTER JOIN T2 consists of their paired rowswhere the join-condition is true and, for each unpaired row of T2, theconcatenation of that row with the null row of T1. All columns derivedfrom T1 allow null values.· The result of T1 FULL OUTER JOIN T2 consists of their paired rows and,for each unpaired row of T2, the concatenation of that row with the nullrow of T1 and, for each unpaired row of T1, the concatenation of that rowwith the null row of T2. All columns derived from T1 and T2 allow nullvalues. 5. Q. How do you add record to a table? A. INSERT into table_name VALUES (‘ALEX’ , 33 , ‘M’); 6. Q. How do you add a column to a table? A. ALTER TABLE Department ADD (AGE, NUMBER); 7. Q. How do you change value of the field? A. UPDATE EMP_table set number = 200 where item_munber = ‘CD’; update name_table set status = 'enable' where phone = '4161112222'; update SERVICE_table set REQUEST_DATE = to_date ('2006-03-04 09:29', 'yyyy-mm-dd hh24:MI') where phone = '4161112222'; 8. Q. What does COMMIT do? A. Saving all changes made by DML statements 9. Q. What is a primary key? A. The column (columns) that has completely unique data throughout the table is known as the primary key field. 10. Q. What are foreign keys? A. Foreign key field – is a field that links one table to another table’s primary or foreign key. 11. Q. What is the main role of a primary key in a table? A. The main role of a primary key in a data table is to maintain the internal integrity of a data table. 12. Q. Can a table have more than one foreign key defined? A. A table can have any number of foreign keys defined. It can have only one primary key defined. 13. Q. List all the possible values that can be stored in a BOOLEAN data field. A. There are only two values that can be stored in a BOOLEAN data field: -1(true) and 0(false). 14 Q. What is the highest value that can be stored in a BYTE data field? A. The highest value that can be stored in a BYTE field is 255. or from -128 to 127. Byte is a set of Bits that represent a single character. Usually there are 8 Bits in a Byte, sometimes more, depending on how the measurement is being made. Each Char requires one byte of memory and can have a value from 0 to 255 (or 0 to 11111111 in binary). 15. Q. How many places to the right of the decimal can be stored in a CURRENCY data field? A. The CURRENCY data type can store up to four places to the right of the decimal. Any data beyond the fourth place will be truncated by Visual Basic without reporting an error. 16. Q. What is a stored procedure? A. A procedure is a group of PL/SQL statements that can be called by a name. Procedures do not return values they perform tasks. 17. Q. Describe how NULLs work in SQL? A. The NULL is how SQL handles missing values. Arifthmetic operation with NULL in SQL will return a NULL. 18. Q. What is Normalization? A. The process of table design is called normalization. 19. Q. What is referential integrity constraints? A. Referential integrity constraints are rules that are partnof the table in a database schema. 20. Q. What is Trigger? A. Trigger will execute a block of procedural code against the database when a table event occurs. A2. A trigger defines a set of actions that are performed in response to an insert, update, or delete operation on a specified table. When such an SQL operation is executed, in this case the trigger has been activated. 21. Q. Which of the following WHERE clauses will return only rows that have a NULL in the PerDiemExpenses column?A. WHERE PerDiemExpenses <> B. WHERE PerDiemExpenses IS NULLC. WHERE PerDiemExpenses = NULLD. WHERE PerDiemExpenses NOT IN (*) A. B is correct � When searching for a NULL value in a column, you must use the keyword IS. No quotes are required around the keyword NULL. 22. Q. You issue the following query:SELECT FirstName FROMStaffListWHERE FirstName LIKE'_A%'Which names would be returned by this query? Choose all that apply.A. AllenB. CLARKC. JACKSOND. David A. C is correct � Two wildcards are used with the LIKE operator. The underscore (_) stands for any one character of any case, and the percent sign (%) stands for any number of characters of any case including none. Because this string starts with an underscore rather than a percent sign, it won't return Allen or Clark because they represent zero and two characters before the "A". If the LIKE string had been "%A%", both of these values would have been returned. David was not returned because all non-wild card characters are case sensitive. Therefore, only strings with an uppercase "A" as their second letter are returned 23. Q. Write a SQL SELECT query that only returns each city only once from Students table?Do you need to order this list with an ORDER BY clause? A. SELECT DISTINCT CityFROM Students; The Distinct keyword automatically sorts all data in ascending order. However, if you want the data sorted in descending order, you have to use an ORDER BY clause 24. Q. Write a SQL SELECT sample of the concatenation operator. A. SELECT LastName ',' FirstName, City FROM Students; 25. Q. How to rename column in the SQL SELECT query? A. SELECT LastName ',' FirstName AS "Student Name", City AS "Home City" "FROM StudentsORDER BY "Student Name"



26. Q. Write SQL SELECT example how you limiting the rows returned with a WHERE clause. A. SELECT InstructorID, Salary FROM Instructors WHERE Salary > 5400 AND Salary < 6600; 27. Q. Write SQL SELECT query that returns the first and last name of each instructor, the Salary, and gives each of them a number. A. SELECT FirstName, LastName, Salary, ROWNUM FROM Instructors; 28. Q. Which of the following functions can be used only with numeric values? (Choose all that apply.)A. AVGB. MINC. LENGTHD. SUME. ROUND A. A and D � Only A and D are correct. The MIN function works with any character, numeric, or date datatype. The LENGTH function is a character function that returns the number of letters in a character value. The ROUND function works with both numeric and date values. 29. Q. Which function do you use to remove all padded characters to the right of a character value in a column with a char datatype?A. RTRIMB. RPADC. TRIM A. C � The TRIM function is used to remove padded spaces. LTRIM and RTRIM functions were included in earlier versions of Oracle, but Oracle 8i has replaced them with a single TRIM function 30. Q. Which statement do you use to eliminate padded spaces between the month and day values in a function TO_CHAR(SYSDATE,'Month, DD, YYYY') ? A. To remove padded spaces, you use the "fm" prefix before the date element that contains the spaces. TO_CHAR(SYSDATE,'fmMonth DD, YYYY') 31. Q. Is the WHERE clause must appear always before the GROUP BY clause in SQL SELECT ? A. Yes.The proper order for SQL SELECT clauses is: SELECT, FROM, WHERE, GROUP BY, HAVING, ORDER BY. Only the SELECT and FROM clause are mandatory. 32. Q. How Oracle executes a statement with nested subqueries? A. When Oracle executes a statement with nested subqueries,it always executes the innermost query first. This query passes its results to the next query and so on until it reaches the outermost query. It is the outermost query that returns a result set. 33. Q. Which operator do you use to return all of the rows from one query except rows are returned in a second query? A. You use the MINUS operator to return all rows from one query except where duplicate rows are found in a second query. The UNION operator returns all rows from both queries minus duplicates. The UNION ALL operator returns all rows from both queries including duplicates. The INTERSECT operator returns only those rows that exist in both queries. 34. Q. How you will create a column alias? (Oracle 8i) A. The AS keyword is optional when specifying a column alias. You must enclose the column alias in double quotes when the alias contains a space or lowercase letters. If you specify an alias in lowercase letters without double quotes, the alias will appear in uppercase. 35 Q. Which of the following statements are Data Manipulation Language commands?A. INSERTB. UPDATEC. GRANTD. TRUNCATEE. CREATE A. A and B � The INSERT and UPDATE statements are Data Manipulation Language (DML) commands. GRANT is a Data Control Language (DCL) command. TRUNCATE and CREATE are Data Definition Language (DDL) commands 36. Question. What is Oracle locking? A. Oracle uses locking mechanisms to protect data from being destroyed by concurrent transactions. 37. Question. What Oracle lock modes do you know? A. Oracle has two lock modes: shared or exclusive. Shared locks are set on database resources so that many transactions can access the resource. Exclusive locks are set on resources that ensure one transaction has exclusive access to the database resource 38. Question. What is query optimization? A. Query optimization is the part of the query process in which the database system compares different query strategies and chooses the one with the least expected cost 39. Question. What are the main components of Database management systems software. A. The database management system software includes components for storage management, concurrency control, transaction processing, database manipulation interface, database definition interface,and database control interface. 40. Question. What are the main attributes of database management system? A. A database management system is composed of five elements: computer hardware, software, data, people (users), and operations procedures. 41. Question. What is transaction? A. A transaction is a collection of applications code and database manipulation code bound into an indivisible unit of execution.it consists from:BEGIN-TRANSACTION NameCodeEND TRANSACTION Name 42. Question. What databases do you know?Informix DB2 SQL Oracle 43. Question. Explain SQL SELECT example: select j.FILE_NUM from DB_name.job j, DB_name.address awhere j.JOB_TYPE ='C' AND j.COMPANY_NAME = 'TEST6' AND j.OFFICE_ID = '101' AND j.ACTIVE_IND = 'Y' AND a.ADDRESS_STATUS_ID = 'H' AND a.OFFICE_ID = '101' AND a.FILE_NUM = j.FILE_NUM order by j.FILE_NUM; Answer: j and a aliases for table names. this is outer joint select statament from two tables. 44. Q. Describe some Conversion Functions that you know A. TO_CHAR converts a number / date to a string. TO_DATE converts a string (representing a date) to a date. TO_NUMBER converts a character string containing digits to a numeric data type, it accepts one parameter which is a column value or a string literal 45. Q. Describe some Group Functions that you know A. 1) The COUNT function tells you how many rows were in the result set. SELECT COUNT(*) FROM TESTING.QA 2) The AVG function tells you the average value of a numeric column. SELECT MAX(SALARY) FROM TESTING.QA 3) The MAX and MIN functions tell you the maximum and minimum value of a numeric column. SELECT MIN(SALARY) FROM TESTING.QA 4) The SUM function tells you the sum value of a numeric column. SELECT SUM(SALARY) FROM TESTING.QA 46. Question. What does DML stand for? A. DML is Data Manipulation Language statements. (SELECT) 47. Question. What does DDL stand for? A. DDL is Data Definition Language statements. (CREATE) 48. Question. What does DCL stand for? A. DCL is Data Control Language statements. (COMMIT) 49. Question: Describe SQL comments. A. SQL comments are introduced by two consecutive hyphens (--) and ended by the end of the line. 50. Q. In what sequence SQL statement are processed? A. The clauses of the subselect are processed in the following sequence (DB2):1. FROM clause2. WHERE clause3. GROUP BY clause4. HAVING clause5. SELECT clause6. ORDER BY clause7. FETCH FIRST clause 51. Q. Describe TO_DATE function. A. The TO_DATE function returns a timestamp from a character string that has been interpreted using a character template.TO_DATE is a synonym for TIMESTAMP_FORMAT. 52. Question: In the domain table we have status as a numeric value from 01 to 04 and we have text definition of these values in the design document. Write SQL query to see the result as a text definitions that is corresponded to these values. (DB2) A. select TB1.member_id, TB1.bu_id, TB1.program, TB2.num, case TB1.status when '01' then 'Auto renew' when '02' then 'Expired' when '03' then 'Sold' when '04' then ‘Terminated’ else TB_name.status end from DB_name.TB_name1 TB1, DB_name.TB_name2 TB2 where TB1.program in ('com', 'org') and TB1.member_role = '100' order by TB1.member_id fetch first 30 rows only
Which of the following statements contains an error?
SELECT * FROM emp WHERE empid = 493945;
SELECT empid FROM emp WHERE empid= 493945;
SELECT empid FROM emp;
SELECT empid WHERE empid = 56949 AND lastname = ‘SMITH’;
Which of the following correctly describes how to specify a column alias?
Place the alias at the beginning of the statement to describe the table.
Place the alias after each column, separated by white space, to describe the column.
Place the alias after each column, separated by a comma, to describe the column.
Place the alias at the end of the statement to describe the table.
The NVL function
Assists in the distribution of output across multiple columns.
Allows the user to specify alternate output for non-null column values.
Allows the user to specify alternate output for null column values.
Nullifies the value of the column output.
Output from a table called PLAYS with two columns, PLAY_NAME and AUTHOR, is shown below. Which of the following SQL statements produced it?
PLAY_TABLE————————————-“Midsummer Night’s Dream”, SHAKESPEARE“Waiting For Godot”, BECKETT“The Glass Menagerie”, WILLIAMS
SELECT play_name author FROM plays;
SELECT play_name, author FROM plays;
SELECT play_name’, ‘ author FROM plays;
SELECT play_name’, ‘ author PLAY_TABLE FROM plays;
Issuing the DEFINE_EDITOR=”emacs” will produce which outcome?
The emacs editor will become the SQL*Plus default text editor.
The emacs editor will start running immediately.
The emacs editor will no longer be used by SQL*Plus as the default text editor.
The emacs editor will be deleted from the system.
The user issues the following statement. What will be displayed if the EMPID selected is 60494?
SELECT DECODE(empid,38475, “Terminated”,60494, “LOA”, “ACTIVE”)FROM emp;
60494
LOA
Terminated
ACTIVE
SELECT (TO_CHAR(NVL(SQRT(59483), “INVALID”)) FROM DUAL is a valid SQL statement.
TRUE
FALSE
The appropriate table to use when performing arithmetic calculations on values defined within the SELECT statement (not pulled from a table column) is
EMP
The table containing the column values
DUAL
An Oracle-defined table
Which of the following is not a group function?
avg( )
sqrt( )
sum( )
max( )
Once defined, how long will a variable remain so in SQL*Plus?
Until the database is shut down
Until the instance is shut down
Until the statement completes
Until the session completes
The default character for specifying runtime variables in SELECT statements is
Ampersand
Ellipses
Quotation marks
Asterisk
A user is setting up a join operation between tables EMP and DEPT. There are some employees in the EMP table that the user wants returned by the query, but the employees are not assigned to departments yet. Which SELECT statement is most appropriate for this user?
select e.empid, d.head from emp e, dept d;
select e.empid, d.head from emp e, dept d where e.dept# = d.dept#;
select e.empid, d.head from emp e, dept d where e.dept# = d.dept# (+);
select e.empid, d.head from emp e, dept d where e.dept# (+) = d.dept#;
Developer ANJU executes the following statement: CREATE TABLE animals AS SELECT * from MASTER.ANIMALS; What is the effect of this statement?
A table named ANIMALS will be created in the MASTER schema with the same data as the ANIMALS table owned by ANJU.
A table named ANJU will be created in the ANIMALS schema with the same data as the ANIMALS table owned by MASTER.
A table named ANIMALS will be created in the ANJU schema with the same data as the ANIMALS table owned by MASTER.
A table named MASTER will be created in the ANIMALS schema with the same data as the ANJU table owned by ANIMALS.
User JANKO would like to insert a row into the EMPLOYEE table, which has three columns: EMPID, LASTNAME, and SALARY. The user would like to enter data for EMPID 59694, LASTNAME Harris, but no salary. Which statement would work best?
INSERT INTO employee VALUES (59694,’HARRIS’, NULL);
INSERT INTO employee VALUES (59694,’HARRIS’);
INSERT INTO employee (EMPID, LASTNAME, SALARY) VALUES (59694,’HARRIS’);
INSERT INTO employee (SELECT 59694 FROM ‘HARRIS’);
Which three of the following are valid database datatypes in Oracle? (Choose three.)
CHAR
VARCHAR2
BOOLEAN
NUMBER
Omitting the WHERE clause from a DELETE statement has which of the following effects?
The delete statement will fail because there are no records to delete.
The delete statement will prompt the user to enter criteria for the deletion
The delete statement will fail because of syntax error.
The delete statement will remove all records from the table.
Creating a foreign-key constraint between columns of two tables defined with two different datatypes will produce an error.
TRUE
FALSE
Dropping a table has which of the following effects on a nonunique index created for the table?
No effect.
The index will be dropped.
The index will be rendered invalid.
The index will contain NULL values.
To increase the number of nullable columns for a table,
Use the alter table statement.
Ensure that all column values are NULL for all rows.
First increase the size of adjacent column datatypes, then add the column.
Add the column, populate the column, then add the NOT NULL constraint.
Which line of the following statement will produce an error?
CREATE TABLE goods
(good_no NUMBER,
good_name VARCHAR2 check(good_name in (SELECT name FROM avail_goods)),
CONSTRAINT pk_goods_01
PRIMARY KEY (goodno));
There are no errors in this statement.
MAXVALUE is a valid parameter for sequence creation.
TRUE
FALSE
Which of the following lines in the SELECT statement below contain an error?
SELECT DECODE(empid, 58385, “INACTIVE”, “ACTIVE”) empid
FROM emp
WHERE SUBSTR(lastname,1,1) > TO_NUMBER(’S')
AND empid > 02000
ORDER BY empid DESC, lastname ASC;
There are no errors in this statement.
Which function below can best be categorized as similar in function to an IF-THEN-ELSE statement?
SQRT
DECODE
NEW_TIME
ROWIDTOCHAR
Which two of the following orders are used in ORDER BY clauses? (choose two)
ABS
ASC
DESC
DISC
You query the database with this command
SELECT nameFROM employeeWHERE name LIKE ‘_a%’;
Which names are displayed?
Names starting with “a”
Names starting with “aR
or “A”
Names containing “aR
as second character
Names containing “aR
as any letter except the first
Posted in: General
13 Responses to “SQL interview questions”
db don Says: May 16th, 2005 at 7:55 pm
1) “SELECT empid WHERE empid = 56949 AND lastname = ‘SMITH’;” is incorrect
2) “Place the alias after each column, separated by white space, to describe the column.” Correct
3) Ans is 3 it is same as isNull in T SQL
Ajay Kumar Peddireddy Says: February 6th, 2006 at 7:52 am
1)SELECT empid WHERE empid = 56949 AND lastname = ‘SMITH’;2)Place the alias after each column, separated by white space, to describe the column3)Allows the user to specify alternate output for null column values.4)SELECT play_name’, ‘ author PLAY_TABLE FROM plays;5)The emacs editor will become the SQL*Plus default text editor. (Not sure about this answer)6)LOA7)FALSE8)DUAL9)max( )10)Until the statement completes11)Ampersand12)select e.empid, d.head from emp e, dept d where e.dept# (+) = d.dept#;13)A table named ANIMALS will be created in the ANJU schema with the same data as the ANIMALS table owned by MASTER14)INSERT INTO employee VALUES (59694,’HARRIS’, NULL);15) VARCHAR2 , BOOLEAN ,NUMBER16) The delete statement will remove all records from the table.17) TRUE18) The index will be dropped.19) Ensure that all column values are NULL for all rows. (Not sure about this answer)20) SELECT statement is not allowed in CHeck constraint.21)22) No error if all the values are given in single quotes instead of double quotes.23) DECODE24) ASC, DESC25) will give all the enames that has ‘a’ in the second place and followed by any number of characters. _ specifies as a single character and % as many characters.
Mrs Bisht Says: October 17th, 2006 at 11:11 am
1)SELECT empid WHERE empid = 56949 AND lastname = ‘SMITH’;2)Place the alias after each column, separated by white space, to describe the column3)Allows the user to specify alternate output for null column values.4)SELECT play_name’, ‘ author PLAY_TABLE FROM plays;5)The emacs editor will become the SQL*Plus default text editor. (Not sure about this answer)6)LOA7)FALSE8)DUAL9)max( )10)Until the statement completes11)Ampersand12)select e.empid, d.head from emp e, dept d where e.dept# (+) = d.dept#;13)A table named ANIMALS will be created in the ANJU schema with the same data as the ANIMALS table owned by MASTER14)INSERT INTO employee VALUES (59694,’HARRIS’, NULL);15) VARCHAR2 , BOOLEAN ,NUMBER16) The delete statement will remove all records from the table.17) TRUE18) The index will be dropped.19) Ensure that all column values are NULL for all rows. (Not sure about this answer)20) SELECT statement is not allowed in CHeck constraint.21)22) No error if all the values are given in single quotes instead of double quotes.23) DECODE24) ASC, DESC25) will give all the enames that has ‘a’ in the second place and followed by any number of characters. _ specifies as a single character and % as many characters.
Acrien Says: October 28th, 2006 at 7:21 pm
some wrong answers up top.
1. Which of the following statements contains an error?
1. SELECT * FROM emp WHERE empid = 493945;2. SELECT empid FROM emp WHERE empid= 493945;3. SELECT empid FROM emp;*** 4. SELECT empid WHERE empid = 56949 AND lastname = ‘SMITH’;
No from clause.
2 Which of the following correctly describes how to specify a column alias?
1. Place the alias at the beginning of the statement to describe the table.*** 2. Place the alias after each column, separated by white space, to describe the column.3. Place the alias after each column, separated by a comma, to describe the column.4. Place the alias at the end of the statement to describe the table.
3 The NVL function
1. Assists in the distribution of output across multiple columns.2. Allows the user to specify alternate output for non-null column values.****3. Allows the user to specify alternate output for null column values.4. Nullifies the value of the column output.
4 Output from a table called PLAYS with two columns, PLAY_NAME and AUTHOR, is shown below. Which of the following SQL statements produced it?
PLAY_TABLE————————————-“Midsummer Night’s Dream”, SHAKESPEARE“Waiting For Godot”, BECKETT“The Glass Menagerie”, WILLIAMS
1. SELECT play_name author FROM plays;2. SELECT play_name, author FROM plays;3. SELECT play_name’, ‘ author FROM plays;***4. SELECT play_name’, ‘ author PLAY_TABLE FROM plays;
1 will produce titleauthor2 will produce title author3 will produce title, author but column name will be play_name’,'author
5 Issuing the DEFINE_EDITOR=”emacs” will produce which outcome?
****1. The emacs editor will become the SQL*Plus default text editor.2. The emacs editor will start running immediately.3. The emacs editor will no longer be used by SQL*Plus as the default text editor.4. The emacs editor will be deleted from the system.
6 The user issues the following statement. What will be displayed if the EMPID selected is 60494?
SELECT DECODE(empid,38475, “Terminated”,60494, “LOA”, “ACTIVE”)FROM emp;
1. 60494*** 2. LOA3. Terminated4. ACTIVEdecode says if(empid = 38475, output ‘terminatedif(empid = 60409, output ‘loa’(for everything else, output ‘active’)
7 SELECT (TO_CHAR(NVL(SQRT(59483), “INVALID”)) FROM DUAL is a valid SQL statement.
1. TRUE**** 2. FALSE
Cannot set value to another datatype when using NVL, hence if SQRT(59483) is null somehow, you must assign it a number, “invalid” is a string.
8 The appropriate table to use when performing arithmetic calculations on values defined within the SELECT statement (not pulled from a table column) is
1. EMP2. The table containing the column values***3. DUAL4. An Oracle-defined table
Dual is a dummy table.
9 Which of the following is not a group function?
1. avg( )*****2. sqrt( )3. sum( )4. max( )
all other functions can work on more than one row of data.
10 Once defined, how long will a variable remain so in SQL*Plus?
1. Until the database is shut down2. Until the instance is shut down**** 3. Until the statement completes**** 4. Until the session completes
This one depends on how you defined it. If you define variable using & then 3, && then 4.
11 The default character for specifying runtime variables in SELECT statements is
*** 1. Ampersand2. Ellipses3. Quotation marks4. Asterisk
This is basic syntax. In pl/sql though, this is compile time, not run time.
12 A user is setting up a join operation between tables EMP and DEPT. There are some employees in the EMP table that the user wants returned by the query, but the employees are not assigned to departments yet. Which SELECT statement is most appropriate for this user?
1. select e.empid, d.head from emp e, dept d;2. select e.empid, d.head from emp e, dept d where e.dept# = d.dept#;*****3. select e.empid, d.head from emp e, dept d where e.dept# = d.dept# (+);4. select e.empid, d.head from emp e, dept d where e.dept# (+) = d.dept#;
Always put the (+) on the deficient side, so since emp has more data that cannot be matched in dept table, dept table has less data than emp hence it is the deficient side!
13 Developer ANJU executes the following statement: CREATE TABLE animals AS SELECT * from MASTER.ANIMALS; What is the effect of this statement?
1. A table named ANIMALS will be created in the MASTER schema with the same data as the ANIMALS table owned by ANJU.2. A table named ANJU will be created in the ANIMALS schema with the same data as the ANIMALS table owned by MASTER.**** 3. A table named ANIMALS will be created in the ANJU schema with the same data as the ANIMALS table owned by MASTER.4. A table named MASTER will be created in the ANIMALS schema with the same data as the ANJU table owned by ANIMALS.
refer to another’s table by using schemaname.objectname.
14 User JANKO would like to insert a row into the EMPLOYEE table, which has three columns: EMPID, LASTNAME, and SALARY. The user would like to enter data for EMPID 59694, LASTNAME Harris, but no salary. Which statement would work best?
****1. INSERT INTO employee VALUES (59694,’HARRIS’, NULL);2. INSERT INTO employee VALUES (59694,’HARRIS’);3. INSERT INTO employee (EMPID, LASTNAME, SALARY) VALUES (59694,’HARRIS’);4. INSERT INTO employee (SELECT 59694 FROM ‘HARRIS’);
The only statement that does not contain error.
15 Which three of the following are valid database datatypes in Oracle? (Choose three.)
***1. CHAR***2. VARCHAR23. BOOLEAN***4. NUMBEROracle does not support boolean. Boolean can be represented by 0 or 1 and therefore no need to create a datatype for it.
16 Omitting the WHERE clause from a DELETE statement has which of the following effects?
1. The delete statement will fail because there are no records to delete.2. The delete statement will prompt the user to enter criteria for the deletion3. The delete statement will fail because of syntax error.***4. The delete statement will remove all records from the table.
If select statement does not have a where clause, it would select all rows. Hence delete without where clause would delete all rows.
17 Creating a foreign-key constraint between columns of two tables defined with two different datatypes will produce an error.
***1. TRUE2. FALSE
18 Dropping a table has which of the following effects on a nonunique index created for the table?
1. No effect.***2. The index will be dropped.3. The index will be rendered invalid.4. The index will contain NULL values.
19 To increase the number of nullable columns for a table,
***1. Use the alter table statement.2. Ensure that all column values are NULL for all rows.3. First increase the size of adjacent column datatypes, then add the column.4. Add the column, populate the column, then add the NOT NULL constraint.
Bad or badly phrased question, but to increase the number of any kind of column, you’d use alter table statement.
20 Which line of the following statement will produce an error?
1. CREATE TABLE goods2. (good_no NUMBER,***3. good_name VARCHAR2 check(good_name in (SELECT name FROM avail_goods)),4. CONSTRAINT pk_goods_015. PRIMARY KEY (goodno));6. There are no errors in this statement.
Cannot have subquery in check.
21 MAXVALUE is a valid parameter for sequence creation.
***1. TRUE2. FALSE
22 Which of the following lines in the SELECT statement below contain an error?
1. SELECT DECODE(empid, 58385, “INACTIVE”, “ACTIVE”) empid2. FROM emp***3. WHERE SUBSTR(lastname,1,1) > TO_NUMBER(’S’)4. AND empid > 020005. ORDER BY empid DESC, lastname ASC;6. There are no errors in this statement.
cannot convert a letter to a number.
23 Which function below can best be categorized as similar in function to an IF-THEN-ELSE statement?
1. SQRT***2. DECODE3. NEW_TIME4. ROWIDTOCHAR
24 Which two of the following orders are used in ORDER BY clauses? (choose two)
1. ABS***2. ASC***3. DESC4. DISC
25 You query the database with this command
SELECT nameFROM employeeWHERE name LIKE ‘_a%’;
Which names are displayed?(should read as following I think)1. Names starting with “a”2. Names starting with “aR or “A”***3. Names containing “aR” as second character4. Names containing “aR” as any letter except the first
It still doesn’t make much sense as ‘aR’ cannot both be second character. the pattern would be to have lower case ‘a’ as second character, followed by anything and start with anything.
pravasis Says: March 6th, 2007 at 4:32 am
1.SELECT empid WHERE empid = 56949 AND lastname = ‘SMITH’; (no from)2.Place the alias after each column, separated by white space, to describe the column.3.Allows the user to specify alternate output for null column values.4.SELECT play_name’, ‘ author PLAY_TABLE FROM plays;5.The emacs editor will become the SQL*Plus default text editor.6.LOA(decode(column_name,if_value1,show_value1,if_value2,show_value2,rest)7.false(Datatype mismatch)8.DUAL9.sqrt(mathematical function)10.Until the session completes11.Ampersand12.select e.empid, d.head from emp e, dept d where e.dept# (+) = d.dept#; (left outer join)13.A table named ANIMALS will be created in the ANJU schema with the same data as the ANIMALS table owned by MASTER.14.INSERT INTO employee VALUES (59694,’HARRIS’, NULL);15.CHAR,VARCHAR2,NUMBER16.The delete statement will remove all records from the table.17.TRUE18.The index will be dropped.19.Ensure that all column values are NULL for all rows.20.good_name VARCHAR2 check(good_name in (SELECT name FROM avail_goods)), (select may not be allowed)21.TRUE22.WHERE SUBSTR(lastname,1,1) > TO_NUMBER(’S’) (datatype mismatch)23.DECODE24.ASC DESC25.a as second character
Thiyagu Says: March 24th, 2007 at 10:55 am
how to add salary of two tables and store into a result in any one tablei need this output
salarycolumn of emp salarycolumn of emp result1100 1200 1300
johnny Says: June 12th, 2007 at 8:30 am
Hi Thiyagu,
This is johnny…the answer for ur query…if u hav any queries plz do let me know…leave a comment
PRE-REQUISITE:CREATE 2 TABLES(EMP1,EMP2) BASED ON EMP TABLE.AND ADD COLUMN (result NUMBER(6)) in EMP1
– PROGRAM STARTS FROM HEREDECLAREV_SAL1 NUMBER;V_SAL2 NUMBER;V_RESULT NUMBER;V_EMPNO1 NUMBER:=7654;V_EMPNO2 NUMBER:=7369;BEGINSELECT SAL INTO V_SAL1 FROM EMP1 WHERE EMPNO=V_EMPNO1;SELECT SAL INTO V_SAL2 FROM EMP2 WHERE EMPNO=V_EMPNO2;V_RESULT := V_SAL1 + V_SAL2 ;DBMS_OUTPUT.PUT_LINE(’RESULT IS:’V_RESULT);– SENDING THE RESULT INTO EMP1 TABLEUPDATE EMP1 SET RESULT = V_RESULT WHERE EMPNO=V_EMPNO1;END;
Srikanth Says: July 9th, 2007 at 7:47 am
1.4. SELECT empid WHERE empid = 56949 AND lastname = ‘SMITH’;
2.2. Place the alias after each column, separated by white space, to describe the column.
3. The NVL function
3. Allows the user to specify alternate output for null column values.
4.4. SELECT play_name’, ‘ author PLAY_TABLE FROM plays;
5.1. The emacs editor will become the SQL*Plus default text editor.
6.2. LOA
7.2. FALSE ( invalid number error occurred checked).
8.3. DUAL
9.2. sqrt( )single row function
10.4. Until the session completes
11.1. Ampersand
12.4. select e.empid, d.head from emp e, dept d where e.dept# (+) = d.dept#;
13.3. A table named ANIMALS will be created in the ANJU schema with the same data as the ANIMALS table owned by MASTER.
14.1. INSERT INTO employee VALUES (59694,’HARRIS’, NULL);
15. Which three of the following are valid database datatypes in Oracle? (Choose three.)1. CHAR2. VARCHAR24. NUMBERboolean is an pl/sql datatype in oracle.
16.4. The delete statement will remove all records from the table.
17.1. TRUE
18.2. The index will be dropped.
19.1. Use the alter table statement.
20.3. good_name VARCHAR2 check(good_name in (SELECT name FROM avail_goods)),
21.1. TRUE
22.3. WHERE SUBSTR(lastname,1,1) > TO_NUMBER(’S’)
23.2. DECODE
24.2. ASC3. DESC
25.5. as second character
gaurav gaur Says: October 22nd, 2007 at 11:22 am
LTER procedure gaurav@tablename nvarchar(40)asdeclare @column_name nvarchar(34)declare @gencode nvarchar(234)declare @sqlstring varchar(234)declare @commandobjectname nvarchar(2345)set @gencode=”set @commandobjectname=’mycommand’select @gencode=@gencode +char(13)+’mycommand.parameters.addwithvalue(”@’+column_name+’”‘+column_name+’)’ from information_columns.columns where table_name=@tablenameprint @gencode
gaurav gaur Says: October 22nd, 2007 at 11:26 am
aLTER procedure gaurav@tablename nvarchar(40)asdeclare @column_name nvarchar(34)declare @gencode nvarchar(234)declare @sqlstring varchar(234)declare @commandobjectname nvarchar(2345)set @gencode=”set @commandobjectname=’mycommand’select @gencode=@gencode +char(13)+’mycommand.parameters.addwithvalue(”@’+column_name+’”‘+column_name+’)’ from information_columns.columns where table_name=@tablenameprint @gencode“this stored procedure id best those who are working as asp.net developer bcz in .net we use to cm.parametrs.addwithvalue(”columnname’@columnname)we did not write any above code if we foolow above stored procedure just execute itwith the help of command exe gaurav ‘tablename”happy coding
masti Says: December 2nd, 2007 at 9:32 pm
.SELECT empid WHERE empid = 56949 AND lastname = ‘SMITH’; (no from)2.Place the alias after each column, separated by white space, to describe the column.3.Allows the user to specify alternate output for null column values.4.SELECT play_name’, ‘ author PLAY_TABLE FROM plays;5.The emacs editor will become the SQL*Plus default text editor.6.LOA(decode(column_name,if_value1,show_value1,if_value2,show_value2,rest)7.false(Datatype mismatch)8.DUAL9.sqrt(mathematical function)10.Until the session completes11.Ampersand12.select e.empid, d.head from emp e, dept d where e.dept# (+) = d.dept#; (left outer join)13.A table named ANIMALS will be created in the ANJU schema with the same data as the ANIMALS table owned by MASTER.14.INSERT INTO employee VALUES (59694,’HARRIS’, NULL);15.CHAR,VARCHAR2,NUMBER16.The delete statement will remove all records from the table.17.TRUE18.The index will be dropped.19.Ensure that all column values are NULL for all rows.20.good_name VARCHAR2 check(good_name in (SELECT name FROM avail_goods)), (select may not be allowed)21.TRUE22.WHERE SUBSTR(lastname,1,1) > TO_NUMBER(’S’) (datatype mismatch)23.DECODE24.ASC DESC25.a as second character
preppy Says: January 2nd, 2008 at 2:20 am
Which of the following statements contains an error?
SELECT empid WHERE empid = 56949 AND lastname = ‘SMITH’;
Which of the following correctly describes how to specify a column alias?
Place the alias after each column, separated by white space, to describe the column.
The NVL functionAllows the user to specify alternate output for null column values.
Output from a table called PLAYS with two columns, PLAY_NAME and AUTHOR, is shown below. Which of the following SQL statements produced it?
PLAY_TABLE————————————-“Midsummer Night’s Dream”, SHAKESPEARE“Waiting For Godot”, BECKETT“The Glass Menagerie”, WILLIAMS
SELECT play_name’, ‘ author PLAY_TABLE FROM plays;
Issuing the DEFINE_EDITOR=”emacs” will produce which outcome?
The emacs editor will become the SQL*Plus default text editor.
The user issues the following statement. What will be displayed if the EMPID selected is 60494?
SELECT DECODE(empid,38475, “Terminated”,60494, “LOA”, “ACTIVE”)FROM emp;
LOA
SELECT (TO_CHAR(NVL(SQRT(59483), “INVALID”)) FROM DUAL is a valid SQL statement.
TRUE
The appropriate table to use when performing arithmetic calculations on values defined within the SELECT statement (not pulled from a table column) isEMPDUAL
Which of the following is not a group function?sqrt( )
Once defined, how long will a variable remain so in SQL*Plus?
Until the session completes
The default character for specifying runtime variables in SELECT statements is
Ampersand
A user is setting up a join operation between tables EMP and DEPT. There are some employees in the EMP table that the user wants returned by the query, but the employees are not assigned to departments yet. Which SELECT statement is most appropriate for this user?
select e.empid, d.head from emp e, dept d where e.dept# = d.dept# (+);
Developer ANJU executes the following statement: CREATE TABLE animals AS SELECT * from MASTER.ANIMALS; What is the effect of this statement?
A table named ANIMALS will be created in the ANJU schema with the same data as the ANIMALS table owned by MASTER.
User JANKO would like to insert a row into the EMPLOYEE table, which has three columns: EMPID, LASTNAME, and SALARY. The user would like to enter data for EMPID 59694, LASTNAME Harris, but no salary. Which statement would work best?
INSERT INTO employee (EMPID, LASTNAME, SALARY) VALUES (59694,’HARRIS’);
Which three of the following are valid database datatypes in Oracle? (Choose three.)
CHARVARCHAR2NUMBER
Omitting the WHERE clause from a DELETE statement has which of the following effects?
The delete statement will remove all records from the table.
Creating a foreign-key constraint between columns of two tables defined with two different datatypes will produce an error.
TRUE
Dropping a table has which of the following effects on a nonunique index created for the table?
The index will be dropped.
To increase the number of nullable columns for a table,
Use the alter table statement.
Which line of the following statement will produce an error?
good_name VARCHAR2 check(good_name in (SELECT name FROM avail_goods)),
MAXVALUE is a valid parameter for sequence creation.
TRUE (not sure)
Which of the following lines in the SELECT statement below contain an error?
WHERE SUBSTR(lastname,1,1) > TO_NUMBER(’S’)
Which function below can best be categorized as similar in function to an IF-THEN-ELSE statement?
DECODE
Which two of the following orders are used in ORDER BY clauses? (choose two)
ASCDESC
You query the database with this command
SELECT nameFROM employeeWHERE name LIKE ‘_a%’;
Which names are displayed?
RaiS Says: January 16th, 2008 at 6:37 am
1.Which of the following statements contains an error?SELECT empid WHERE empid = 56949 AND lastname = ‘SMITH’;
2.Which of the following correctly describes how to specify a column alias?Place the alias after each column, separated by white space, to describe the column.
3.The NVL functionAllows the user to specify alternate output for non-null column values.
4.Output from a table called PLAYS with two columns, PLAY_NAME and AUTHOR, is shown below. Which of the following SQL statements produced it?
PLAY_TABLE————————————-“Midsummer Night’s Dream”, SHAKESPEARE“Waiting For Godot”, BECKETT“The Glass Menagerie”, WILLIAMSNone of the above
5.Issuing the DEFINE_EDITOR=”emacs” will produce which outcome?
The emacs editor will become the SQL*Plus default text editor.
6. The user issues the following statement. What will be displayed if the EMPID selected is 60494?
SELECT DECODE(empid,38475, “Terminated”,60494, “LOA”, “ACTIVE”)FROM emp;
LOA
Which of the following is not a group function?sqrt( )
Once defined, how long will a variable remain so in SQL*Plus?Until the session completes
The default character for specifying runtime variables in SELECT statements isAmpersand
A user is setting up a join operation between tables EMP and DEPT. There are some employees in the EMP table that the user wants returned by the query, but the employees are not assigned to departments yet. Which SELECT statement is most appropriate for this user?select e.empid, d.head from emp e, dept d where e.dept# (+) = d.dept#;
Developer ANJU executes the following statement: CREATE TABLE animals AS SELECT * from MASTER.ANIMALS; What is the effect of this statement?A table named ANIMALS will be created in the ANJU schema with the same data as the ANIMALS table owned by MASTER.
User JANKO would like to insert a row into the EMPLOYEE table, which has three columns: EMPID, LASTNAME, and SALARY. The user would like to enter data for EMPID 59694, LASTNAME Harris, but no salary. Which statement would work best?INSERT INTO employee VALUES (59694,’HARRIS’);
Which three of the following are valid database datatypes in Oracle? (Choose three.)CHARVARCHAR2NUMBER
Omitting the WHERE clause from a DELETE statement has which of the following effects?The delete statement will remove all records from the table.
Creating a foreign-key constraint between columns of two tables defined with two different datatypes will produce an error.TRUE
Dropping a table has which of the following effects on a nonunique index created for the table?The index will be dropped.
Which line of the following statement will produce an error?CREATE TABLE goods(good_no NUMBER,good_name VARCHAR2 check(good_name in (SELECT name FROM avail_goods)),CONSTRAINT pk_goods_01PRIMARY KEY (goodno));There are no errors in this statement.PRIMARY KEY (goodno));
MAXVALUE is a valid parameter for sequence creation.TRUEFALSE
Which two of the following orders are used in ORDER BY clauses? (choose two)ASCDESC
You query the database with this command
SELECT nameFROM employeeWHERE name LIKE ‘_a%’;
Which names are displayed?Names containing “aRas second character
. How do you implement one-to-one, one-to-many and many-to-many relationships while designing tables?One-to-One relationship can be implemented as a single table and rarely as two tables with primary and foreign key relationships.One-to-Many relationships are implemented by splitting the data into two tables with primary key and foreign key relationships.Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table.It will be a good idea to read up a database designing fundamentals text book.
2. What's the difference between a primary key and a unique key?Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn't allow NULLs, but nique key allows one NULL only.3. What are user defined datatypes and when you should go for them?User defined datatypes let you extend the base SQL Server datatypes by providing a descriptive name, and format to the database. Take for example, in your database, there is a column called Flight_Num which appears in many tables. In all these tables it should be varchar(8). In this case you could create a user defined datatype called Flight_num_type of varchar(8) and use it across all your tables.
4. What is bit datatype and what's the information that can be stored inside a bit column?Bit datatype is used to store boolean information like 1 or 0 (true or false). Untill SQL Server 6.5 bit datatype could hold either a 1 or 0 and there was no support for NULL. But from SQL Server 7.0 onwards, bit datatype can represent a third state, which is NULL.5. Define candidate key, alternate key, composite keyA candidate key is one that can identify each row of a table uniquely. Generally a candidate key becomes the primary key of the table. If the table has more than one candidate key, one of them will become the primary key, and the rest are called alternate keys.A key formed by combining at least two or more columns is called composite key.6. What are defaults? Is there a column to which a default can't be bound?A default is a value that will be used by a column, if no value is supplied to that column while inserting data. IDENTITY columns and timestamp columns can't have defaults bound to them. See CREATE DEFUALT in books online.7. What is a transaction and what are ACID properties?A transaction is a logical unit of work in which, all the steps must be performed or none. ACID stands for Atomicity, Consistency, Isolation, Durability. These are the properties of a transaction. For more information and explanation of these properties, see SQL Server books online or any RDBMS fundamentals text book.
8. Explain different isolation levelsAn isolation level determines the degree of isolation of data between concurrent transactions. The default SQL Server isolation level is Read Committed. Here are the other isolation levels (in the ascending order of isolation): Read Uncommitted, Read Committed, Repeatable Read, Serializable. See SQL Server books online for an explanation of the isolation levels. Be sure to read about SET TRANSACTION ISOLATION LEVEL, which lets you customize the isolation level at the connection level.
9. CREATE INDEX myIndex ON myTable(myColumn)What type of Index will get created after executing the above statement?Non-clustered index. Important thing to note: By default a clustered index gets created on the primary key, unless specified otherwise.10. What's the maximum size of a row?8060 bytes. Don't be surprised with questions like 'what is the maximum number of columns per table'. Check out SQL Server books online for the page titled: "Maximum Capacity Specifications".11. Explain Active/Active and Active/Passive cluster configurationsHopefully you have experience setting up cluster servers. But if you don't, at least be familiar with the way clustering works and the two clustering configurations Active/Active and Active/Passive. SQL Server books online has enough information on this topic and there is a good white paper available on Microsoft site.12. Explain the architecture of SQL ServerThis is a very important question and you better be able to answer it if consider yourself a DBA. SQL Server books online is the best place to read about SQL Server architecture. Read up the chapter dedicated to SQL Server Architecture.13. What is lock escalation?Lock escalation is the process of converting a lot of low level locks (like row locks, page locks) into higher level locks (like table locks). Every lock is a memory structure too many locks would mean, more memory being occupied by locks. To prevent this from happening, SQL Server escalates the many fine-grain locks to fewer coarse-grain locks. Lock escalation threshold was definable in SQL Server 6.5, but from SQL Server 7.0 onwards it's dynamically managed by SQL Server.14. What's the difference between DELETE TABLE and TRUNCATE TABLE commands?DELETE TABLE is a logged operation, so the deletion of each row gets logged in the transaction log, which makes it slow. TRUNCATE TABLE also deletes all the rows in a table, but it won't log the deletion of each row, instead it logs the deallocation of the data pages of the table, which makes it faster. Of course, TRUNCATE TABLE can be rolled back.15. Explain the storage models of OLAPCheck out MOLAP, ROLAP and HOLAP in SQL Server books online for more infomation.16. What are the new features introduced in SQL Server 2000 (or the latest release of SQL Server at the time of your interview)? What changed between the previous version of SQL Server and the current version?This question is generally asked to see how current is your knowledge. Generally there is a section in the beginning of the books online titled "What's New", which has all such information. Of course, reading just that is not enough, you should have tried those things to better answer the questions. Also check out the section titled "Backward Compatibility" in books online which talks about the changes that have taken place in the new version.1. What are constraints? Explain different types of constraintsConstraints enable the RDBMS enforce the integrity of the database automatically, without needing you to create triggers, rule or defaults.Types of constraints: NOT NULL, CHECK, UNIQUE, PRIMARY KEY, FOREIGN KEYFor an explanation of these constraints see books online for the pages titled: "Constraints" and "CREATE TABLE", "ALTER TABLE"2. What is an index? What are the types of indexes? How many clustered indexes can be created on a table? I create a separate index on each column of a table. what are the advantages and disadvantages of this approach?Indexes in SQL Server are similar to the indexes in books. They help SQL Server retrieve the data quicker.Indexes are of two types. Clustered indexes and non-clustered indexes. When you craete a clustered index on a table, all the rows in the table are stored in the order of the clustered index key. So, there can be only one clustered index per table. Non-clustered indexes have their own storage separate from the table data storage. Non-clustered indexes are stored as B-tree structures (so do clustered indexes), with the leaf level nodes having the index key and it's row locater. The row located could be the RID or the Clustered index key, depending up on the absence or presence of clustered index on the table.If you create an index on each column of a table, it improves the query performance, as the query optimizer can choose from all the existing indexes to come up with an efficient execution plan. At the same t ime, data modification operations (such as INSERT, UPDATE, DELETE) will become slow, as every time data changes in the table, all the indexes need to be updated. Another disadvantage is that, indexes need disk space, the more indexes you have, more disk space is used.3. What is RAID and what are different types of RAID configurations?RAID stands for Redundant Array of Inexpensive Disks, used to provide fault tolerance to database servers. There are six RAID levels 0 through 5 offering different levels of performance, fault tolerance. MSDN has some information about RAID levels and for detailed information, check out the RAID advisory board's homepage.4. What are the steps you will take to improve performance of a poor performing query?This is a very open ended question and there could be a lot of reasons behind the poor performance of a query. But some general issues that you could talk about would be: No indexes, table scans, missing or out of date statistics, blocking, excess recompilations of stored procedures, procedures and triggers without SET NOCOUNT ON, poorly written query with unnecessarily complicated joins, too much normalization, excess usage of cursors and temporary tables.Some of the tools/ways that help you troubleshooting performance problems are: SET SHOWPLAN_ALL ON, SET SHOWPLAN_TEXT ON, SET STATISTICS IO ON, SQL Server Profiler, Windows NT /2000 Performance monitor, Graphical execution plan in Query Analyzer.Download the white paper on performance tuning SQL Server from Microsoft web site. Don't forget to check out sql-server-performance.com5. What are the steps you will take, if you are tasked with securing an SQL Server?Again this is another open ended question. Here are some things you could talk about: Preferring NT authentication, using server, database and application roles to control access to the data, securing the physical database files using NTFS permissions, using an unguessable SA password, restricting physical access to the SQL Server, renaming the Administrator account on the SQL Server computer, disabling the Guest account, enabling auditing, using multiprotocol encryption, setting up SSL, setting up firewalls, isolating SQL Server from the web server etc.6. What is a deadlock and what is a live lock? How will you go about resolving deadlocks?Deadlock is a situation when two processes, each having a lock on one piece of data, attempt to acquire a lock on the other's piece. Each process would wait indefinitely for the other to release the lock, unless one of the user processes is terminated. SQL Server detects deadlocks and terminates one user's process.A livelock is one, where a request for an exclusive lock is repeatedly denied because a series of overlapping shared locks keeps interfering. SQL Server detects the situation after four denials and refuses further shared locks. A livelock also occurs when read transactions monopolize a table or page, forcing a write transaction to wait indefinitely.7. What is blocking and how would you troubleshoot it?Blocking happens when one connection from an application holds a lock and a second connection requires a conflicting lock type. This forces the second connection to wait, blocked on the first.Read up the following topics in SQL Server books online: Understanding and avoiding blocking, Coding efficient transactions.8. Explain CREATE DATABASE syntaxMany of us are used to craeting databases from the Enterprise Manager or by just issuing the command: CREATE DATABAE MyDB. But what if you have to create a database with two filegroups, one on drive C and the other on drive D with log on drive E with an initial size of 600 MB and with a growth factor of 15%? That's why being a DBA you should be familiar with the CREATE DATABASE syntax. Check out SQL Server books online for more information.9. How to restart SQL Server in single user mode? How to start SQL Server in minimal configuration mode?SQL Server can be started from command line, using the SQLSERVR.EXE. This EXE has some very important parameters with which a DBA should be familiar with. -m is used for starting SQL Server in single user mode and -f is used to start the SQL Server in minimal configuration mode. Check out SQL Server books online for more parameters and their explanations.10. As a part of your job, what are the DBCC commands that you commonly use for database maintenance?DBCC CHECKDB, DBCC CHECKTABLE, DBCC CHECKCATALOG, DBCC CHECKALLOC, DBCC SHOWCONTIG, DBCC SHRINKDATABASE, DBCC SHRINKFILE etc. But there are a whole load of DBCC commands which are very useful for DBAs. Check out SQL Server books online for more information.11. What are statistics, under what circumstances they go out of date, how do you update them?Statistics determine the selectivity of the indexes. If an indexed column has unique values then the selectivity of that index is more, as opposed to an index with non-unique values. Query optimizer uses these indexes in determining whether to choose an index or not while executing a query.Some situations under which you should update statistics:1) If there is significant change in the key values in the index2) If a large amount of data in an indexed column has been added, changed, or removed (that is, if the distribution of key values has changed), or the table has been truncated using the TRUNCATE TABLE statement and then repopulated3) Database is upgraded from a previous versionLook up SQL Server books online for the following commands: UPDATE STATISTICS, STATS_DATE, DBCC SHOW_STATISTICS, CREATE STATISTICS, DROP STATISTICS, sp_autostats, sp_createstats, sp_updatestats12. What are the different ways of moving data/databases between servers and databases in SQL Server?There are lots of options available, you have to choose your option depending upon your requirements. Some of the options you have are: BACKUP/RESTORE, dettaching and attaching databases, replication, DTS, BCP, logshipping, INSERT...SELECT, SELECT...INTO, creating INSERT scripts to generate data.13. Explain different types of BACKUPs available in SQL Server? Given a particular scenario, how would you go about choosing a backup plan?Types of backups you can create in SQL Sever 7.0+ are Full database backup, differential database backup, transaction log backup, filegroup backup. Check out the BACKUP and RESTORE commands in SQL Server books online. Be prepared to write the commands in your interview. Books online also has information on detailed backup/restore architecture and when one should go for a particular kind of backup.14. What is database replication? What are the different types of replication you can set up in SQL Server?Replication is the process of copying/moving data between databases on the same or different servers. SQL Server supports the following types of replication scenarios:o Snapshot replicationo Transactional replication (with immediate updating subscribers, with queued updating subscribers)o Merge replication See SQL Server books online for indepth coverage on replication. Be prepared to explain how different replication agents function, what are the main system tables used in replication etc.15. How to determine the service pack currently installed on SQL Server?The global variable @@Version stores the build number of the sqlservr.exe, which is used to determine the service pack installed. To know more about this process visitWhat are cursors? Explain different types of cursors. What are the disadvantages of cursors? How can you avoid cursors?Cursors allow row-by-row processing of the resultsets.Types of cursors: Static, Dynamic, Forward-only, Keyset-driven. See books online for more information.Disadvantages of cursors: Each time you fetch a row from the cursor, it results in a network roundtrip, where as a normal SELECT query makes only one rowundtrip, however large the resultset is. Cursors are also costly because they require more resources and temporary storage (results in more IO operations). Furthere, there are restrictions on the SELECT statements that can be used with some types of cursors.Most of the times, set based operations can be used instead of cursors. Here is an example:If you have to give a flat hike to your employees using the following criteria:Salary between 30000 and 40000 -- 5000 hikeSalary between 40000 and 55000 -- 7000 hikeSalary between 55000 and 65000 -- 9000 hikeIn this situation many developers tend to use a cursor, determine each employee's salary and update his salary according to the above formula. But the same can be achieved by multiple update statements or can be combined in a single UPDATE statement as shown below:UPDATE tbl_emp SET salary =CASE WHEN salary BETWEEN 30000 AND 40000 THEN salary + 5000WHEN salary BETWEEN 40000 AND 55000 THEN salary + 7000WHEN salary BETWEEN 55000 AND 65000 THEN salary + 10000ENDAnother situation in which developers tend to use cursors: You need to call a stored procedure when a column in a particular row meets certain condition. You don't have to use cursors for this. This can be achieved using WHILE loop, as long as there is a unique key to identify each row.17. Write down the general syntax for a SELECT statements covering all the optionsHere's the basic syntax: (Also checkout SELECT in books online for advanced syntax).SELECT select_list[INTO new_table_]FROM table_source[WHERE search_condition][GROUP BY group_by_expression][HAVING search_condition][ORDER BY order_expression [ASC DESC] ]18. What is a join and explain different types of joinsJoins are used in queries to explain how different tables are related. Joins also let you select data from a table depending upon data from another table.Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs.OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER JOINS.19. Can you have a nested transaction?Yes, very much. Check out BEGIN TRAN, COMMIT, ROLLBACK, SAVE TRAN and @@TRANCOUNT20. What is an extended stored procedure? Can you instantiate a COM object by using T-SQL?An extended stored procedure is a function within a DLL (written in a programming language like C, C++ using Open Data Services (ODS) API) that can be called from T-SQL,just the way we call normal stored procedures using the EXEC statement. See books online to learn how to create extended stored procedures and how to add them to SQL Server.Yes, you can instantiate a COM (written in languages like VB, VC++) object from T-SQL by using sp_OACreate stored procedure. Also see books online for sp_OAMethod, sp_OAGetProperty, sp_OASetProperty, sp_OADestroy.21. What is the system function to get the current user's user id?USER_ID().Also check out other system functions like USER_NAME(), SYSTEM_USER, SESSION_USER, CURRENT_USER, USER, SUSER_SID(), HOST_NAME().22. What are triggers? How many triggers you can have on a table? How to invoke a trigger on demand?Triggers are special kind of stored procedures that get executed automatically when an INSERT, UPDATE or DELETE operation takes place on a table.In SQL Server 6.5 you could define only 3 triggers per table, one for INSERT, one for UPDATE and one for DELETE. From SQL Server 7.0 onwards, this restriction is gone, and you could create multiple triggers per each action. But in 7.0 there's no way to control the order in which the triggers fire. In SQL Server 2000 you could specify which trigger fires first or fires last using sp_settriggerorderTriggers can't be invoked on demand. They get triggered only when an associated action (INSERT, UPDATE, DELETE) happens on the table on which they are defined.Triggers are generally used to implement business rules, auditing. Triggers can also be used to extend the referential integrity checks, but wherever possible, use constraints for this purpose, instead of triggers, as constraints are much faster.Till SQL Server 7.0, triggers fire only after the data modification operation happens. So in a way, they are called post triggers. But in SQL Server 2000 you could create pre triggers also. Search SQL Server 2000 books online for INSTEAD OF triggers.23. There is a trigger defined for INSERT operations on a table, in an OLTP system. The trigger is written to instantiate a COM object and pass the newly insterted rows to it for some custom processing. What do you think of this implementation? Can this be implemented better?Instantiating COM objects is a time consuming process and since you are doing it from within a trigger, it slows down the data insertion process. Same is the case with sending emails from triggers. This scenario can be better implemented by logging all the necessary data into a separate table, and have a job which periodically checks this table and does the needful.24. What is a self join? Explain it with an exampleSelf join is just like any other join, except that two instances of the same table will be joined in the query. Here is an example: Employees table which contains rows for normal employees as well as managers. So, to find out the managers of all the employees, you need a self join.CREATE TABLE emp(empid int,mgrid int,empname char(10))INSERT emp SELECT 1,2,'Vyas'INSERT emp SELECT 2,3,'Mohan'INSERT emp SELECT 3,NULL,'Shobha'INSERT emp SELECT 4,2,'Shridhar'INSERT emp SELECT 5,2,'Sourabh'SELECT t1.empname [Employee], t2.empname [Manager]FROM emp t1, emp t2WHERE t1.mgrid = t2.empid Here's an advanced query using a LEFT OUTER JOIN that even returns the employees without managers (super bosses)SELECT t1.empname [Employee], COALESCE(t2.empname, 'No manager') [Manager]FROM emp t1LEFT OUTER JOINemp t2ONt1.mgrid = t2.empid