|The SQL Procedure|
|sql-expression <NOT> LIKE sql-expression <ESCAPE character-expression>|
is described in sql-expression.
is an sql-expression that evaluates to a single character. The operands of character-expression must be character or string literals.
Note: If you use an ESCAPE clause, then the pattern-matching specification must be a quoted string or quoted concatenated string; it cannot contain column names.
The LIKE condition selects rows by comparing character strings with a pattern-matching specification. It resolves to true and displays the matched strings if the left operand matches the pattern specified by the right operand.
The ESCAPE clause is used to search for literal instances of the percent (%) and underscore (_) characters, which are usually used for pattern matching.
|Patterns for Searching|
Patterns consist of three classes of characters:
matches any single character.
matches any sequence of zero or more characters.
matches that character.
matches a three-letter word, so it has no matches here.
|Searching for Literal % and _|
Because the % and _ characters have special meaning in the context of the LIKE condition, you must use the ESCAPE clause to search for these character literals in the input character string.
The condition like 'a_%' matches app , a_% , and a__ , because the underscore (_) in the search pattern matches any single character (including the underscore), and the percent (%) in the search pattern matches zero or more characters, including '%' and '_'.
The condition like 'a_%' escape '_' matches none of the values, because the escape character (_) specifies that the pattern search for an 'a' followed by a literal '%', which does not apply to any of these values.
|Searching for Mixed-Case Strings|
To search for mixed-case strings, use the UPCASE function to make all the names uppercase before entering the LIKE condition:
Note: When you are using the % character, be aware of the effect of trailing blanks. You might have to use the TRIM function to remove trailing blanks in order to match values.