Tricky SQL Interview Questions

SQL Interview Questions

How to insert 10 default records in SQL Table. For example suppose we have Student Table with columns Name, Address and other. Write a query to insert default value in one go.

INSERT INTO mytable DEFAULT VALUES

GO 10

What is GO keyword in SQL?

GO keyword is not associated with SQL but it is property of SQL Server Management Studio. GO can be understand simply for following example.

Student with Mark on their T-Shirt 1,2,3,4,5,6,7,8,9,10 and 11,12….20 are ready to run in an event but when it is said student from 1 to 10 Go then they start running but students from 11 to 20 wait until they are not said.

So it is batch separator in SQL.

What is Temp table and Temp variable in SQL and why they are used?

1.      Temp Table store location is Tempdb while Temp variable storage location if not specified is current database.

2.      Table variables can only be accessed within the batch and scope in which they are declared. Temp Tables are accessible within child batches.

3.      Temp table can’t be used in function while Table variable can be used.

4.      Table variable don’t support Identity insert, altered or truncated while Temp table can do it.

5.      Indexing is similar on Temp table as normal table while Temp variable can have indexing only when primary and unique key is defined.

Consider a table Human with Name and Gender as columns, write a query to update male to female and vice versa.

Update Human case when Gender=’male’ then ‘Female’  else ‘Male’ end

How Trigger works?

As per the syntax of Trigger

create trigger [trigger_name]

[before | after] 

{insert | update | delete} 

on [table_name] 

[for each row] 

[trigger_body]

It run on three events happens on table insert, update and delete. So when if we insert any data in table it will invoke insert trigger which is free to execute before or after.