SQL: Visual QuickStart Guide

Filtering Rows with WHERE

The result of each SELECT statement so far has included every row in the table (for the specified columns). You can use the WHERE clause to filter unwanted rows from the result. This filtering capability gives the SELECT statement its real power. In a WHERE clause, you specify a search condition that comprises one or more conditions that need to be satisfied by the rows of a table. A condition, or predicate, is a logical expression that evaluates to true, false, or unknown. (The unknown result arises from nulls; see the next section.) Rows for which the condition is true are included in the result; rows for which the condition is false or unknown are excluded.

SQL provides operators that express different types of conditions ...