SQL EXISTS operator checks the existence of result of a subquery or more record.

EXISTS Operator Conditions

• SQL EXISTS query result is a BOOLEAN value 'TRUE or FALSE'.
• Use EXISTS operator with SELECT, UPDATE, INSERT, and DELETE.
• SQL NOT EXISTS operator return the result just opposite to EXISTS Operator.

EXISTS Operator Syntax

SELECT column_name(s)
FROM table_name
WHERE EXISTS (
  SELECT column_name
  FROM table_name
  WHERE [condition]);

NOT EXISTS Operator Syntax

SELECT column_name(s)
FROM table_name
WHERE NOT EXISTS (
  SELECT column_name
  FROM table_name
  WHERE [condition]);

EXAMPLE: EXISTS Operator

Customers Table

Simple Customers record table & the name of the table is CUSTOMERS. The Column(s) name of the table like [ID, NAME, EMAIL, ADDRESS, and SALARY]:

Orders Table

This is a sample ORDER table; The columns of the table are [OID, DATE, CUSTOMER_ID, and AMOUNT]:

Example of EXISTS condition with SELECT

SELECT NAME, EMAIL
FROM CUSTOMERS
WHERE EXISTS (
  SELECT *
  FROM ORDERS
  WHERE CUSTOMERS.ID = ORDERS.CUSTOMER_ID);

Result Lokk Like

Example of NOT EXISTS condition with SELECT

SELECT NAME, EMAIL
FROM CUSTOMERS
WHERE NOT EXISTS (
  SELECT *
  FROM ORDERS
  WHERE CUSTOMERS.ID = ORDERS.CUSTOMER_ID);

Result Lokk Like

SQL SUBQUERY

A SQL SUBQUERY is also called NESTED Query; The SUBQUERY is frequently used within other queries.

• A SQL SUBQUERY can be used with multiple statements like SELECT, INSERT, UPDATE, DELETE Statements.
• We can use WHERE condition, HAVING Clause, GROUB BY Clause BUT we can't use ORDER BY Clause within a SUBQUERY.