SQL Server series: nested queries

A nested query refers to a query that is nested inside another query statement. A nested query is also a subquery, in which a subquery is evaluated first in the SELECT clause, and the subquery results as a filter for the outer layer of another query, and the query can be based on one table or multiple tables. Comparison operators can be used in subqueries such as "<", "<=", ">", ">=", and so on.

The operands commonly used in subqueries are any (SOME), all, EXISTS. Subqueries can be added to select, UPDATE, and DELETE statements and can be nested in multiple layers.

1. Using comparison operators

SQL Server series: nested queries