LIKE Predicate (like_predicate)

A LIKE predicate (like_predicate) is a predicate that is used to search for character strings that have a certain pattern. This pattern can be a certain character string or any sequence of characters (whose length may or may not be known).

Syntax

<like_predicate>  ::= <expression> [NOT] LIKE <like_expression> [ESCAPE <expression>]

<like_expression> ::= <expression> | '<pattern_element>...'
<pattern_element> ::= <match_string> | <match_set>

<match_string>    ::= % | X'1F'
<match_set>       ::= <underscore> | X'1E' | <match_char>

<underscore>      ::= _ (underscore)
<match_char>      ::= <!  
every character other than  % | X'1F' | <underscore> | X'1E'  !>

Examples

SQL Tutorial, Searching for Character Strings: LIKE, Negative Conditions: NOT

Explanation

x NOT LIKE y has the same result as NOT(x LIKE y).

Result of x LIKE y

x or y are NULL values

x LIKE y is undefined

x and y are non-NULL values

x LIKE y is either true or false

x can be split into substrings with the result that:

A substring of x is a sequence of 0,1, or more contiguous characters, and each character of x belongs to exactly one substring.

The number of substrings of x and y is identical.

If the nth pattern element (pattern_element) of y is a sequence of characters and the nth substring of x is a sequence of 0 or more characters.

x LIKE y is true

<expression>

The  expression  in the like_expression must return an alphanumeric value or a date or time value.

<pattern_element>

If a match_string is specified, this position in the search pattern can be replaced by any number of characters.

If a match_set is specified, this position in the search pattern can be replaced by the exact number of characters specified in the match_set .

If an underscore or X'1E' is used, this position in the pattern can be replaced by any one character.

If match_char is used, this position in the pattern can be replaced by the specified character itself.

ESCAPE

An escape character ESCAPE <expression> must be used if you want to search for an <underscore>, '%', or the hexadecimal value X'1E' or X'1F' in the LIKE predicate.

If ESCAPE <expression> is specified, the corresponding expression must return an alphanumeric value that consists of just one character. If this escape character is contained in the like_expression , the following character must be one of the special characters <underscore>, %, X’1E’, or X’1F’. This special character is then seen as standing for itself.