postgreSQL EXISTS Operator

The postgreSQL EXISTS operator is used to check the presence of any record in a subquery. If the subquery returns one or more records than EXISTS operator returns true. In case the subquery returns no row, the result is of EXISTS is false. It can be used in a SELECT, UPDATE, INSERT or DELETE statement.EXISTS is often used with the correlated subquery.

EXISTS Operator Syntax :

The syntax of the EXISTS  Operator is −
SELECT column_name(s) 
FROM table_name
WHERE EXISTS 
(SELECT column_name(s) 
FROM table_name
WHERE condition);
The syntax of the NOT EXISTS  Operator is −
SELECT column_name(s) 
FROM table_name
WHERE NOT EXISTS 
(SELECT column_name(s) 
FROM table_name
WHERE condition);

EXISTS Operator Example :

Consider the Customer table with the following records -

Consider the Order table with the following records -

TEST CASE 1:- The following code is an example, which would fetch the Name, Address from Customer table where Customer.ID = Order.CustomerID.

lfcdb=# SELECT Name, Address 
FROM Customer
WHERE EXISTS (SELECT * 
FROM Order 
WHERE Customer.ID = Order.CustomerID);

The result for the respective postgreSQL query is as follows −

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