Pattern Matching
................
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 below. 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 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:
* `.' matches any single character.
* A character class `[...]' matches any character within the
brackets. For example, `[abc]' matches `a', `b', or `c'. To name
a range of characters, use a dash. `[a-z]' matches any lowercase
letter, whereas `[0-9]' matches any digit.
* `*' matches zero or more instances of the thing preceding it. For
example, `x*' matches any number of `x' characters, `[0-9]*'
matches any number of digits, and `.*' matches any number of
anything.
* Regular expressions are case sensitive, but you can use a
character class to match both lettercases if you wish. For
example, `[aA]' matches lowercase or uppercase `a' and `[a-zA-Z]'
matches any letter in either case.
* The pattern matches if it occurs anywhere in the value being
tested. (SQL patterns match only if they match the entire value.)
* To anchor a pattern so that it must match the beginning or end of
the value being tested, use `^' at the beginning or `$' at the end
of the pattern.
To demonstrate how extended regular expressions work, the `LIKE' queries
shown above are rewritten below to use `REGEXP'.
To find names beginning with `b', use `^' to match the beginning of the
name:
mysql> SELECT * FROM pet WHERE name REGEXP "^b";
+--------+--------+---------+------+------------+------------+
| name | owner | species | sex | birth | death |
+--------+--------+---------+------+------------+------------+
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
| Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 |
+--------+--------+---------+------+------------+------------+
Prior to MySQL Version 3.23.4, `REGEXP' is case sensitive, and the
previous query will return no rows. To match either lowercase or
uppercase `b', use this query instead:
mysql> SELECT * FROM pet WHERE name REGEXP "^[bB]";
From MySQL 3.23.4 on, to force a `REGEXP' comparison to be case
sensitive, use the `BINARY' keyword to make one of the strings a binary
string. This query will match only lowercase `b' at the beginning of a
name:
mysql> SELECT * FROM pet WHERE name REGEXP BINARY "^b";
To find names ending with `fy', use `$' to match the end of the name:
mysql> SELECT * FROM pet WHERE name REGEXP "fy$";
+--------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+--------+--------+---------+------+------------+-------+
| Fluffy | Harold | cat | f | 1993-02-04 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
+--------+--------+---------+------+------------+-------+
To find names containing a lowercase or uppercase `w', use this query:
mysql> SELECT * FROM pet WHERE name REGEXP "w";
+----------+-------+---------+------+------------+------------+
| name | owner | species | sex | birth | death |
+----------+-------+---------+------+------------+------------+
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Bowser | Diane | dog | m | 1989-08-31 | 1995-07-29 |
| Whistler | Gwen | bird | NULL | 1997-12-09 | NULL |
+----------+-------+---------+------+------------+------------+
Because a regular expression pattern matches if it occurs anywhere in
the value, it is not necessary in the previous query to put a wild card
on either side of the pattern to get it to match the entire value like
it would be if you used a SQL pattern.
To find names containing exactly five characters, use `^' and `$' 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 |
+-------+--------+---------+------+------------+-------+