SQL Pocket Guide, 3rd Edition

Predicates

Predicates are conditions you write in the WHERE, ON, and HAVING clauses of an 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 1-13 lists the available comparison operators. Some operators, such as IN and EXISTS, are more fully described in later subsections. Regular-expression operators are described under Regular Expressions. Operators for dealing with nulls are described under Nulls.

Table 1-13. 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 and NOT EXISTS to test for the existence of rows matching a set of conditions that you specify. For ...