Postgres Subqueries
Subqueries as Expressions
Scalar Subquery
Results in a single row
Multi-Row Subquery
Results in multiple rows, tipically used in the where clause with operators such as IN, NOT, EXISTS, ANY and ALL.
Correlated Subquery
A uncorrelated sub-query is a type of sub-query where the inner query doesn’t depend upon the outer query for its execution.
Uncorrelated Subquery
A correlated sub-query is a type of query where the inner query depends upon the outcome of the outer query in order to perform its execution.