Saturday, October 20, 2012

Use regular expressions in MySQL SELECT statements

A very cool and powerful capability in MySQL and other databases is the ability to incorporate regular expression syntax when selecting data. The regular expresion support in MySQL is extensive. This recipe reviews regular expression use in MySQL and lists the supported regular expression metacharacters.

The basic syntax to use regular expressions in a MySQL query is:

SELECT something FROM table WHERE column REGEXP 'regexp'

For example, to select all columns from the table events where the values in the column id end with 5587, use:

SELECT * FROM events WHERE id REGEXP '5587$'

A more elaborate example selects all columns of the table reviews where the values in the column description contain the word excellent:

SELECT * FROM reviews WHERE description REGEXP '[[:<:]]excellent[[:>:]]'

MySQL allows the following regular expression metacharacters:

. match any character ? match zero or one
* match zero or more
+ match one or more
{n} match n times
{m,n} match m through n times
{n,} match n or more times
^ beginning of line
$ end of line
[[:<:]] match beginning of words
[[:>:]] match ending of words
[:class:] match a character class
i.e., [:alpha:] for letters
[:space:] for whitespace
[:punct:] for punctuation
[:upper:] for upper case letters
[abc] match one of enclosed chars
[^xyz] match any char not enclosed
| separates alternatives

MySQL interprets a backslash (\) character as an escape character. To use a backslash in a regular expression, you must escape it with another backslash (\\).

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