SQL Pocket Guide, 2nd Edition

Predicates

Predicates are conditions you write in the WHERE, ON, and HAVING clauses of a SQL statement that determine which rows are affected, or returned, by that statement. For example, use the predicate name = 'Wagner Falls' to return data for only that particular waterfall:

SELECT u.zone, u.northing, u.easting
FROM upfall u
WHERE name = 'Wagner Falls';

Table 14 lists the available comparison operators. Some operators, such as IN and EXISTS, are more fully described in upcoming subsections. Regular-expression operators are described later in the "Regular Expressions" section. Operators for dealing with nulls are described in "Nulls.”

Table 14. Comparison operators

Operator	Description
!=, <>	Tests for inequality
<	Tests for less than
<=	Tests for less than or equal to
<=>	Null-safe test for equality; supported only by MySQL
=	Tests for equality
>	Tests for greater than
>=	Tests for greater than or equal to
BETWEEN	Tests whether a value lies within a given range
EXISTS	Tests whether rows exist matching conditions that you specify
IN	Tests whether a value is contained in a set of values that you specify or that are returned by a subquery
IS [NOT] NULL	Tests for nullity
LIKE	Tests whether a value matches a pattern
REGEXP, RLIKE	Regular-expression comparison operator; supported only by MySQL
REGEXP_LIKE	Tests whether a value matches the pattern described by a regular expression; supported only by Oracle

EXISTS Predicates

Use EXISTS ...