Top 10 SQL Interview Questions: Part 1

 Hello Friends,

I will be providing few Interview questions every week so that easily to learn. If get any doubts comment and if you have any questions please feel free to ask.

1. What are the different subsets of SQL?

• DDL (Data Definition Language) – It allows you to perform various operations on the database such as CREATE, ALTER and DELETE objects.                                             For example create table,Alter Table or delete.
• DML ( Data Manipulation Language) – It allows you to access and manipulate data. It helps you to insert, update, delete and retrieve data from the database.                         For example insert data into table and update data or delete.
• DCL ( Data Control Language) – It allows you to control access to the database. Example – Grant, Revoke access permissions.

2. What is the difference between UNION and UNION ALL?

        The difference between UNION and UNION ALL is that UNION will omit duplicate

         records  whereas UNION ALL will include duplicate records.

         Union will be used to merge 2 table result with same structure. 

        For example need to get data of 2 tables with same structure will use Union that

        will merge both results and give it as one.

3. What are joins in SQL?

       A JOIN clause is used to combine rows from two or more tables, based on a                         related column between them. It is used to merge two tables or retrieve data from there. There are 4 joins in SQL namely:

• Inner Join
• Right Join
• Left Join
• Full Join

4.Write a sql query to get department wise highest salary?

    SELECT DEPID, MAX(SALARY) FROM EMPLOYEE GROUP BY DEPID

5. Write a sql query to get employees greater than 10000?

    SELECT * FROM EMPLOYEE WHERE SALARY>10000

6. How to create new GUID in Sql server?

    We have a datatype called UNIQUEIDENTIFIER that accepts GUID. To generate a new

     GUID    use following code.

   SELECT NEWID() AS GUID

7. Difference between Stored Procedure and a function?

    The function must return a value but in Stored Procedure it is optional. Even a procedure can return       zero or n values. Functions can have only input parameters for it whereas Procedures can have input or output parameters. Functions can be called from Procedure whereas Procedures cannot be called from a Function

8. What is a constraint and most used constraints in SQL?

     SQL constraints are used to specify rules for the data in a table

     Constraints can be column level or table level. Column level constraints apply to a column, and     table level constraints apply to the whole table.

NOT NULL - Ensures that a column cannot have a NULL value

UNIQUE - Ensures that all values in a column are different

PRIMARY KEY - A combination of a NOT NULL and UNIQUE. Uniquely identifies each row in a table

FOREIGN KEY - Uniquely identifies a row/record in another table

CHECK - Ensures that all values in a column satisfies a specific condition

DEFAULT - Sets a default value for a column when no value is specified

INDEX - Used to create and retrieve data from the database very quickly

9. Find the employee records with Name “Amar” it can be upper case or lower case “AMAR”,”aMar”,”amar”

SELECT * from Employees WHERE UPPER(EmpName) like '%AMAR%';

10. Can a Table have 2 Primary Keys?

 Table can have only one primary key, which may consist of single or multiple fields. When multiple fields are used as a primary key, they are called a composite key. If a table has a primary key defined on any field(s), then you cannot have two records having the same value of that field(s).

Code to create composite key.

DROP TABLE #TEMP1

CREATE TABLE #TEMP1(

ID INT  ,

DONE INT ,

 PRIMARY KEY (ID, DONE)

)

Thanks for reading friends. If any questions on above, feel free to comment.

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