What is a Nested Query in SQL?

nested select sql A subquery can be nested inside the WHERE or HAVING clause of an outer SELECT , INSERT , UPDATE , or DELETE statement.

SQL – Sub Queries

SELECT column_name [, column_name ]
FROM table1 [, table2 ]
WHERE column_name OPERATOR
(SELECT column_name [, column_name ]
FROM table1 [, table2 ]
[WHERE])

Examples of Nested SQL Queries

SELECT AVG(number_of_students)
FROM classes
WHERE member_id IN (
SELECT id
FROM members
WHERE country = 'India' OR country = 'Pakistan');

Consider the UserS table having the following records −

SQL> SELECT *
FROM UserS
WHERE ID IN (SELECT ID
FROM UserS
WHERE BALANCE > 4500) ;

Subqueries with the INSERT Statement

SQL> INSERT INTO UserS_BKP
SELECT * FROM UserS
WHERE ID IN (SELECT ID
FROM UserS) ;

Subqueries with the UPDATE Statement

SQL> UPDATE UserS
SET BALANCE = BALANCE * 0.25
WHERE POINT IN (SELECT POINT FROM UserS_BKP
WHERE POINT >= 27 );

Subqueries with the DELETE Statement

SQL> DELETE FROM UserS
WHERE POINT IN (SELECT POINT FROM UserS_BKP
WHERE POINT >= 27 );

SELECT within SELECT Tutorial

SELECT name FROM cricket
WHERE teams >
(SELECT teams FROM cricket
WHERE name='India')

I hope you get an idea about nested select sql.

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