GUIDE深度 · Deep dive
Subqueries, EXISTS and Window Functions
A subquery can return one value, one column or many rows: = for single values, IN for multiple rows, EXISTS for existence. Window functions rank/accumulate without collapsing rows.
Subqueries
IN (SELECT ...) for multiple rows.
EXISTS (SELECT 1 ...) for existence.
Correlated subqueries reference the outer table.
Window
ROW_NUMBER() OVER (PARTITION BY ... ORDER BY ...).
Window functions do not reduce rows.
FAQ
Can a subquery return multiple columns?
Yes, but compare with row values/EXISTS.
What is a CTE?
A named temporary result set declared with WITH.