SQL

Most Essential And Frequently Asked Interview Questions And Answer

Q:How can we optimize a table?

Ans:

OPTIMIZE command is use for optimize a table.

 OPTIMIZE TABLE `users` 

 

Q:What is a view in SQL?

Ans:

SQL | View

View in SQL is a kind of virtual table. It does not physical exists in our database but have rows and column as there we have in real database table. we can create a view by selecting fields from one or tables present in the database. A View can have all the rows of a table or specific rows based on certain condition.

View Detials

Q:What is the difference between BETWEEN and IN operator in SQL?

Ans:

SQL | difference between BETWEEN and IN operator

The BETWEEN operator select all records between the given range whereas IN operator select all matching records  given with WHERE clause.

View Detials

Q:What is the difference between primary key and unique constraints?

Ans:

SQL | Difference between primary key and unique constraints

There is only one primary key in a table. It creates the cluster index automatically and it cannot have NULL value
where as there can be multiple unique constraints in a table. It dose not creates the cluster index automatically and it can have NULL value

Q:Write an SQL query to find names of employee start with 'A'?

Ans:

SQL | LIKE operator

The LIKE operator of SQL is used for such kind of operations. It is used to fetch filtered data by searching for a particular pattern in where clause.

View Detials

Q:Find nth largest salary from employees table?

Ans:

By using following query we can find out the nth largest salary from employees table.

 SELECT salary FROM `employees` ORDER BY salary DESC LIMIT 1 OFFSET n-1

In the above query n is replaced by any number where n >= 1. Suppose you want to find fifth highest salary then you have to use offset = 5-1 i.e.: 4

The query will be:

 SELECT salary FROM `employees` ORDER BY salary DESC LIMIT 1 OFFSET 4