Joe Celko's SQL for Smarties, 3rd Edition

Chapter 12. LIKE Predicate

THE LIKE PREDICATE IS a string pattern-matching test with the syntax:

<like predicate> ::=
    <match value> [NOT] LIKE <pattern>
        [ESCAPE <escape character>]

<match value> ::= <character value expression>
<pattern> ::= <character value expression>
<escape character> ::= <character value expression>

The expression M NOT LIKE P is equivalent to NOT (M LIKE P), which follows the usual syntax pattern in SQL. Two wildcards are allowed in the <pattern> string. They are the ‘%’ and ‘_’ characters. The ‘_’ character represents a single arbitrary character; the ‘%’ character represents an arbitrary substring, possibly of length zero. Notice that there is no way to represent zero or one arbitrary character. This is not the case ...