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MySQL provides standard SQL pattern matching as well as a form of
pattern matching based on extended regular expressions similar to those used
by Unix utilities such as vi
, grep
, and sed
.
SQL pattern matching allows you to use `_' to match any single
character and `%' to match an arbitrary number of characters (including
zero characters). In MySQL, SQL patterns are case-insensitive by
default. Some examples are shown here. Note that you do not use =
or <>
when you use SQL patterns; use the LIKE
or NOT
LIKE
comparison operators instead.
To find names beginning with `b':
mysql> SELECT * FROM pet WHERE name LIKE "b%"; +--------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+------------+ | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | +--------+--------+---------+------+------------+------------+ |
To find names ending with `fy':
mysql> SELECT * FROM pet WHERE name LIKE "%fy"; +--------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+-------+ | Fluffy | Harold | cat | f | 1993-02-04 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +--------+--------+---------+------+------------+-------+ |
To find names containing a `w':
mysql> SELECT * FROM pet WHERE name LIKE "%w%"; +----------+-------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+------------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | | Whistler | Gwen | bird | NULL | 1997-12-09 | NULL | +----------+-------+---------+------+------------+------------+ |
To find names containing exactly five characters, use fives instances of the `_' pattern character:
mysql> SELECT * FROM pet WHERE name LIKE "_____"; +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+ |
The other type of pattern matching provided by MySQL uses extended
regular expressions. When you test for a match for this type of pattern, use
the REGEXP
and NOT REGEXP
operators (or RLIKE
and
NOT RLIKE
, which are synonyms).
Some characteristics of extended regular expressions are:
REGEXP
pattern match succeed if
the pattern matches anywhere in the value being tested.
(This differs from a LIKE
pattern match, which succeeds only if the
pattern matches the entire value.)
To demonstrate how extended regular expressions work, the LIKE
queries
shown previously are rewritten here to use REGEXP
.
To find names beginning with `b', use `^' to match the beginning of the name:
mysql> SELECT * FROM pet WHERE name REGEXP "^b"; +--------+--------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+------------+ | Buffy | Harold | dog | f | 1989-05-13 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | +--------+--------+---------+------+------------+------------+ |
Prior to MySQL Version 3.23.4, REGEXP
is case-sensitive,
and the previous query will return no rows. In this case, to match either
lowercase or uppercase `b', use this query instead:
mysql> SELECT * FROM pet WHERE name REGEXP "^[bB]"; |
From MySQL 3.23.4 on, if you really want to force a REGEXP
comparison to
be case-sensitive, use the BINARY
keyword to make one of the
strings a binary string. This query will match only lowercase `b'
at the beginning of a name:
mysql> SELECT * FROM pet WHERE name REGEXP BINARY "^b"; |
To find names ending with `fy', use `$' to match the end of the name:
mysql> SELECT * FROM pet WHERE name REGEXP "fy$"; +--------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +--------+--------+---------+------+------------+-------+ | Fluffy | Harold | cat | f | 1993-02-04 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +--------+--------+---------+------+------------+-------+ |
To find names containing a `w', use this query:
mysql> SELECT * FROM pet WHERE name REGEXP "w"; +----------+-------+---------+------+------------+------------+ | name | owner | species | sex | birth | death | +----------+-------+---------+------+------------+------------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 | | Whistler | Gwen | bird | NULL | 1997-12-09 | NULL | +----------+-------+---------+------+------------+------------+ |
Because a regular expression pattern matches if it occurs anywhere in the value, it is not necessary in the previous query to put a wildcard on either side of the pattern to get it to match the entire value like it would be if you used an SQL pattern.
To find names containing exactly five characters, use `^' and `$' to match the beginning and end of the name, and five instances of `.' in between:
mysql> SELECT * FROM pet WHERE name REGEXP "^.....$"; +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+ |
You could also write the previous query using the `{n}'
"repeat-n
-times" operator:
mysql> SELECT * FROM pet WHERE name REGEXP "^.{5}$"; +-------+--------+---------+------+------------+-------+ | name | owner | species | sex | birth | death | +-------+--------+---------+------+------------+-------+ | Claws | Gwen | cat | m | 1994-03-17 | NULL | | Buffy | Harold | dog | f | 1989-05-13 | NULL | +-------+--------+---------+------+------------+-------+ |
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