A regular expression (regex) is a powerful way of specifying a complex search.
MySQL uses Henry Spencer's implementation of regular expressions, which is aimed to conform to POSIX 1003.2. MySQL uses the extended version.
This is a simplistic reference that skips the details. To get more exact
information, see Henry Spencer's regex(7)
manual page that is
included in the source distribution. See section E Credits.
A regular expression describes a set of strings. The simplest regexp is
one that has no special characters in it. For example, the regexp
hello
matches hello
and nothing else.
Non-trivial regular expressions use certain special constructs so that
they can match more than one string. For example, the regexp
hello|word
matches either the string hello
or the string
word
.
As a more complex example, the regexp B[an]*s
matches any of the
strings Bananas
, Baaaaas
, Bs
and any other string
starting with a B
, ending with an s
, and containing any
number of a
or n
characters in between.
A regular expression may use any of the following special characters/constructs:
^
mysql> select "fo\nfo" REGEXP "^fo$"; -> 0 mysql> select "fofo" REGEXP "^fo"; -> 1
$
mysql> select "fo\no" REGEXP "^fo\no$"; -> 1 mysql> select "fo\no" REGEXP "^fo$"; -> 0
.
mysql> select "fofo" REGEXP "^f.*"; -> 1 mysql> select "fo\nfo" REGEXP "^f.*"; -> 1
a*
a
characters.
mysql> select "Ban" REGEXP "^Ba*n"; -> 1 mysql> select "Baaan" REGEXP "^Ba*n"; -> 1 mysql> select "Bn" REGEXP "^Ba*n"; -> 1
a+
a
characters.
mysql> select "Ban" REGEXP "^Ba+n"; -> 1 mysql> select "Bn" REGEXP "^Ba+n"; -> 0
a?
a
character.
mysql> select "Bn" REGEXP "^Ba?n"; -> 1 mysql> select "Ban" REGEXP "^Ba?n"; -> 1 mysql> select "Baan" REGEXP "^Ba?n"; -> 0
de|abc
de
or abc
.
mysql> select "pi" REGEXP "pi|apa"; -> 1 mysql> select "axe" REGEXP "pi|apa"; -> 0 mysql> select "apa" REGEXP "pi|apa"; -> 1 mysql> select "apa" REGEXP "^(pi|apa)$"; -> 1 mysql> select "pi" REGEXP "^(pi|apa)$"; -> 1 mysql> select "pix" REGEXP "^(pi|apa)$"; -> 0
(abc)*
abc
.
mysql> select "pi" REGEXP "^(pi)*$"; -> 1 mysql> select "pip" REGEXP "^(pi)*$"; -> 0 mysql> select "pipi" REGEXP "^(pi)*$"; -> 1
{1}
{2,3}
a*
a{0,}
.
a+
a{1,}
.
a?
a{0,1}
.
i
and no comma matches a sequence of exactly i
matches of
the atom. An atom followed by a bound containing one integer i
and a comma matches a sequence of i
or more matches of the atom.
An atom followed by a bound containing two integers i
and
j
matches a sequence of i
through j
(inclusive)
matches of the atom.
Both arguments must 0 >= value <= RE_DUP_MAX (default 255)
.
If there are two arguments, the second must be greater than or equal to the
first.
[a-dX]
[^a-dX]
a
, b
,
c
, d
or X
. To include a literal ]
character,
it must immediately follow the opening bracket [
. To include a
literal -
character, it must be written first or last. So
[0-9]
matches any decimal digit. Any character that does not have
a defined meaning inside a []
pair has no special meaning and
matches only itself.
mysql> select "aXbc" REGEXP "[a-dXYZ]"; -> 1 mysql> select "aXbc" REGEXP "^[a-dXYZ]$"; -> 0 mysql> select "aXbc" REGEXP "^[a-dXYZ]+$"; -> 1 mysql> select "aXbc" REGEXP "^[^a-dXYZ]+$"; -> 0 mysql> select "gheis" REGEXP "^[^a-dXYZ]+$"; -> 1 mysql> select "gheisa" REGEXP "^[^a-dXYZ]+$"; -> 0
[[.characters.]]
ch
collating element, then the regular expression [[.ch.]]*c
matches the
first five characters of chchcc
.
[=character_class=]
o
and (+)
are the members of an
equivalence class, then [[=o=]]
, [[=(+)=]]
, and
[o(+)]
are all synonymous. An equivalence class may not be an
endpoint of a range.
[:character_class:]
[:
and :]
stands for the list of all characters belonging
to that class. Standard character class names are:
alnum | digit | punct |
alpha | graph | space |
blank | lower | upper |
cntrl | xdigit |
ctype(3)
manual
page. A locale may provide others. A character class may not be used as an
endpoint of a range.
mysql> select "justalnums" REGEXP "[[:alnum:]]+"; -> 1 mysql> select "!!" REGEXP "[[:alnum:]]+"; -> 0
[[:<:]]
[[:>:]]
ctype(3)
) or an underscore
(_
).
mysql> select "a word a" REGEXP "[[:<:]]word[[:>:]]"; -> 1 mysql> select "a xword a" REGEXP "[[:<:]]word[[:>:]]"; -> 0
mysql> select "weeknights" REGEXP "^(wee|week)(knights|nights)$"; -> 1
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