Nested Query
Introduction Subquery : A SELECT statement located inside another SQL statement (can be inside SELECT, FROM, WHERE, HAVING ). It supplies data for the main query. Nested Query : A term used to describe the structure of the query. When a Subquery resides inside a parent statement, this action is called nesting. Thus, Subquery can be viewed as the component (the child), while Nested query is the structural relationship (the parent containing the child). A statement that contains a subquery has its entire structure referred to as a nested query . Classification Non-correlated Subquery : This type of subquery runs completely independently of the parent statement. Postgres executes this subquery exactly once, using its result to apply to the parent statement. Example: SELECT name, salary FROM employees WHERE salary > (SELECT AVG(salary) FROM employees) Here, SELECT AVG(salary) FROM employees is an independent Subquery that only needs to run once to provide the value for the outer ...