# Subquery in SQL

SQLSQLiteDatabase

A subquery is a query within a query i.e a nested query. It is placed inside a query and its result is used to further evaluate the outer query.

There are some rules that a subquery must follow in SQL. Some of these are −

• The subquery should be placed within parenthesis.
• The subquery can be used with different operators like <,>,<=,>=, IN,BETWEEN etc. Also operators like SELECT, INSERT, DELETE, UPDATE etc. be used.
• The ORDER BY operator cannot be used in the subquery. However, it can be there in the main query.
• A subquery cannot be written with a BETWEEN operator. But the subquery can contain the BETWEEN operator.
• The subquery that returns more than one row cannot be used with all the operators. It can only be used with operators that accept multiple values like IN.

An example of subqueries in SQL is −

<Student>

Student_NumberStudent_NameStudent_PhoneStudent_Marks
1Andrew661592728495
2Sara658365486565
3Harry464756746348
4Megan755476484488
5John343644645425
Select *
from student
where student_marks IN( select student_marks from student where student_marks>50)

This query will return details about all the students who have more than 50 marks i.e. Andrew, Sara and Megan.

Student_NumberStudent_NameStudent_PhoneStudent_Marks
1Andrew661592728495
2Sara658365486565
4Megan755476484488
Published on 03-Aug-2018 11:30:15