expression [ NOT ] SIMILAR TO pattern [ ESCAPE escape-expression ]

To match a substring with the string, use the percentage sign wildcard (%expression). For example, SELECT ... WHERE Description SIMILAR TO 'car' matches only car, not sportscar. However, SELECT ... WHERE Description SIMILAR TO '%car' matches car, sportscar, and any string that ends with car.

When matching against only a sub-character class, you must include the outer square brackets, and the square brackets for the sub-character class. For example, expression SIMILAR TO '[[:digit:]]').

Comparisons are performed character-by-character, unlike the equivalence (=) operator and other operators where the comparison is done string-by-string. For example, when a comparison is done in a UCA collation (CHAR or NCHAR with the collation set to UCA), 'Æ'='AE' is true, but 'Æ' SIMILAR TO 'AE' is false.

For a character-by-character comparison to match, each single character in the expression being searched must match a single character or a wildcard in the SIMILAR TO pattern.

SIMILAR TO use the collation to determine character equivalence and evaluate character class ranges. For example, if the database is case- and accent-insensitive, matches are case- and accent-insensitive. Ranges are also evaluated using the collation sort order.

SIMILAR TO search conditions can be used to compare CHAR and NCHAR strings. In this case, character set conversion is performed so that the comparison is done using a common data type. Then, a character-by-character comparison is performed.

You can specify expression or pattern as an NCHAR string literal by prefixing the quoted value with N (for example, expression SIMILAR TO N'pattern'). You can also use the CAST function to cast the pattern to CHAR or NCHAR (for example, expression SIMILAR TO CAST(pattern AS datatype).

• Regular expressions overview
• Comparisons between CHAR and NCHAR
• String literals
• CAST function [Data type conversion]
• REGEXP search condition
• LIKE search condition
• REGEXP_SUBSTR function [String]
• Regular expressions: Special sub-character classes
• LIKE, REGEXP, and SIMILAR TO search conditions