SQL Important Questions for all interview patterns important and picked by top technical experts

SQL Important Questions:

1> What is DBMS?  & What is RDBMS and difference between both.

2> What is the difference between SQL and MySQL or SQL Server?

3> What is the difference between SQL and PL/SQL?

4> What are various DDL, DML,DCL commands in SQL? Give brief description of their purposes.

5> Is a NULL value same as zero or a blank space? If not then what is the difference?

6> What is constraints in sql and how many constraints are in SQL
Not Null ?
Unique Key (prepare Unique key in details)
Primary Key(prepare Unique key in details)
Foreign Key(prepare Unique key in details)
Check Constraint(prepare Unique key in details)
Index(prepare Unique key in details)
Default(prepare Unique key in details)

7> What is difference between Delete , drop and truncate

8> What is difference between where and having clause

9> What is join and types of join with example?

10> What is Union and Union ALL, difference between both

11> What are the properties and different Types of Sub-Queries?

12> Which TCP/IP port does SQL Server run on?
How can it be changed? Answer: 1433

13> What is index and types of index

14> What is ACID property in database?

15> What is the difference among NULL value, zero and blank space?

16> Which are the different case manipulation functions in SQL?

17> What is the usage of NVL function?

18> Which function is used to return remainder in a division operator in SQL?

19> What is the usage of DISTINCT keyword?

20> What is Normalization and type of normalizations?

21> What is SQL Injection?

22> What is denormalization?

23>  What is a View?

24> What is a Cursor? And type of cursor

25> What are local and global variables and their differences?

26> . What is Datawarehouse?

27> What is OLTP and OLAP and difference between both?

28> What is star Schema and snowflake Schema and difference between

29>  What is Union, minus and Interact commands?

30> What is an ALIAS command?

31> What are aggregate and scalar functions?

32> What is the command used to fetch first 5 characters of the string?

Answer: Select SUBSTRING(StudentName,1,5) as studentname from student

33> How to fetch alternate records from a table?

Answer: Select studentId from (Select rowno, studentId from student) where mod(rowno,2)=0

34>  How to fetch common records from two tables?

Answer: Select studentID from student. <strong>INTERSECT </strong> Select StudentID from Exam

35> How can you create an empty table from an existing table?

Answer: Select * into studentcopy from student where 1=2

36> SQL Query to find second highest salary of Employee ?

Answer: select MAX(Salary) from Employee WHERE Salary NOT IN (select MAX(Salary) from Employ

37> SQL Query to find Max Salary from each department.

Answer:SELECT DeptID, MAX(Salary) FROM Employee  GROUP BY DeptID
38> Write SQL Query to display the current date.

Answer:SELECT GetDate();

39>  Write an SQL Query to check whether date passed to Query is the date of given format or not.

Answer: SELECT  ISDATE('1/08/13') AS "MM/DD/YY";

40>  Write an SQL Query to print the name of the distinct employee whose DOB is between 01/01/1960 to 31/12/1975

Answer:SELECT DISTINCT EmpName FROM Employees WHERE DOB  BETWEEN ‘01/01/1960’ AND ‘31/12/1975’;

41> Write SQL Query to find duplicate rows in a database? and then write SQL query to delete them?

Answer: SELECT * FROM emp a WHERE rowid = (SELECT MAX(rowid) FROM EMP b WHERE a.empno=b.empno)

And To delete:

DELETE FROM emp a WHERE rowid != (SELECT MAX(rowid) FROM emp b WHERE a.empno=b.empno);

42> What is a Composite Key ?

43> What are COMMIT and ROLLBACK in SQL?

44> What is RANK function?

45> What is a materialized view?

46> What is the difference between the NVL and the NVL2 functions?

47> What is the difference between cross joins and natural joins?

48> What is the purpose of the MERGE statement in SQL?

49> What is the difference between VARCHAR2 AND CHAR datatypes?

50>  What is clone Table

51> What is the difference between the RANK() and DENSE_RANK() functions? Provide an example.