PostgreSQL Development Essentials

Using subqueries

A subquery is a query within a query. In other words, a subquery is a SQL query nested inside a larger query. It may occur in a SELECT, FROM, or WHERE clause. In PostgreSQL, a subquery can be nested inside a SELECT, INSERT, UPDATE, DELETE, SET, or DO statement or inside another subquery. It is usually added within the WHERE clause of another SQL SELECT statement. You can use comparison operators, such as >, <, or =. Comparison operators can also be a multiple-row operator, such as IN, ANY, SOME, or ALL. It can be treated as an inner query that is an SQL query placed as a part of another query called as outer query. The inner query is executed before its parent query so that the results of the inner query can be passed to the outer ...