SQL: Visual QuickStart Guide

Comparing a Subquery Value by Using a Comparison Operator

You can use a subquery as a filter in a WHERE clause or HAVING clause by using one of the comparison operators (=, <>, <, <=, >, or >=). The important characteristics of a subquery comparison test are:

• The comparison operators work the same way as they do in other comparisons (refer to Table 4.2 in Chapter 4).

• The subquery can be simple or correlated (see “Simple and Correlated Subqueries” earlier in this chapter).

• The subquery’s SELECT-clause list can include only one expression or column name.

• The compared values must have the same data type or must be implicitly convertible to the same type (see “Converting Data Types with CAST()” in Chapter 5).

• String comparisons may be case-insensitive ...