A subquery, simply put, is a query written as a part of a bigger statement. Think of it as a SELECT statement inside another one. The result of the inner SELECT can then be used in the outer query. Let us take a simple example to illustrate this.
Consider the same source tables as the ones in the joins chapter – authors_tbl and newlang_tbl. We will try to write a query (and a subquery) to display the author of a particular language (Listing 12-1).
SELECT author FROM authors_tbl
WHERE language_id IN
( SELECT id FROM newlang_tbl
WHERE language="Tcl");
Listing 12-1
A simple subquery example
The subquery SELECT ...
