Description of the use of regular expressions in MySql_PHP tutorial

Regular expressions define rules for a string. The simplest regular expression does not contain any reserved words. For example, the regular expression hello only matches the string "hello".
General regular expressions use certain special structures, so they can match more strings. For example, the regular expression hello|word can match both the string "hello" and the string "word".To give a more complex example, the regular expression b[an]*s can match the strings "bananas", "baaaaas", "bs" and any other string starting with b and ending with s, and can include any number of characters in the middle. A combination of a and any number of n.

The following reserved words can be used in a regular expression
^
The matched string starts with the following string
mysql> select "fonfo" regexp "^fo$" ; -> 0 (indicates no match)
mysql> select "fofo" regexp "^fo"; -> 1 (indicates match)
$
The matched string is the previous string Ending
mysql> select "fono" regexp "^fono$"; -> 1 (indicates a match)
mysql> select "fono" regexp "^fo$"; -> 0 (indicates a mismatch)
.
Match any character (including new lines)
mysql> select "fofo" regexp "^f.*"; -> 1 (indicates a match)
mysql> select "fonfo" regexp "^f.*"; -> 1 (indicates matching)
a*
Match any number of a (including empty string)
mysql> select "ban" regexp "^ba*n"; -> 1 (indicates a match)
mysql> select "baaan" regexp "^ba*n"; -> 1 (indicates a match)
mysql> select "bn" regexp "^ba*n"; -> 1 (indicates matching)
a+
Match any number of a (excluding empty string)
mysql> select "ban" regexp "^ba+n"; -> 1 (indicates matching )
mysql> select "bn" regexp "^ba+n"; -> 0 (indicates no match)
a?
Match one or zero a
mysql> select "bn" regexp "^ba?n"; -> 1 (indicates a match)
mysql> select "ban" regexp "^ba?n"; -> 1 (indicates a match)
mysql> select "baan" regexp "^ba?n"; -> 0 (indicates no match)
de|abc
match de or abc
mysql> select "pi" regexp "pi|apa"; -> 1 (Indicates a match)
mysql> select "axe" regexp "pi|apa"; -> 0 (Indicates a mismatch)
mysql> select "apa" regexp "pi|apa"; -> 1 ( Indicates a match)
mysql> select "apa" regexp "^(pi|apa)$"; -> 1 (indicates a match)
mysql> select "pi" regexp "^(pi|apa)$" ; -> 1 (indicates a match)
mysql> select "pix" regexp "^(pi|apa)$"; -> 0 (indicates a mismatch)
(abc)*
matches any Multiple abc (including empty string)
mysql> select "pi" regexp "^(pi)*$"; -> 1 (indicates matching)
mysql> select "pip" regexp "^(pi) *$"; -> 0 (indicates no match)
mysql> select "pipi" regexp "^(pi)*$"; -> 1 (indicates match)
{1}
{ 2,3}
This is a more comprehensive method, which can realize the functions of several previous reserved words
a*
can be written as a{0,}
a+
can be written as a{1,}
a?
can be written as a{0,1}
There is only one integer parameter i in {}, which means that the character can only appear i times; there is an integer in {} type parameter i, followed by a ",", indicating that the character can appear i times or more than i times; there is only one integer parameter i within {}, followed by a ",", and then an integer parameter j, indicating the character It can only appear more than i times and less than j times (including i times and j times). The integer parameter must be greater than or equal to 0 and less than or equal to re_dup_max (default is 255). If there are two parameters, the second must be greater than or equal to the first
[a-dx]
matches "a", "b", "c", "d" or "x"
[ ^a-dx]
Matches any character except "a", "b", "c", "d", "x"."[", "]" must be used in pairs
mysql> select "axbc" regexp "[a-dxyz]"; -> 1 (indicates matching)
mysql> select "axbc" regexp "^[ a-dxyz]$"; -> 0 (indicates no match)
mysql> select "axbc" regexp "^[a-dxyz]+$"; -> 1 (indicates match)
mysql> select "axbc" regexp "^[^a-dxyz]+$"; -> 0 (indicates no match)
mysql> select "gheis" regexp "^[^a-dxyz]+$"; -> ; 1 (indicates a match)
mysql> select "gheisa" regexp "^[^a-dxyz]+$"; -> 0 (indicates a mismatch)
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[[.characters.]]
represents the order of comparison elements. The order of characters within brackets is unique. But wildcards can be included in the brackets, so it can match more characters. For example: the regular expression [[.ch.]]*c matches the first five characters of chchcc.
[=character_class=]
represents an equal class and can replace other equal elements in the class, including itself. For example, if o and (+) are members of an equal class, then [[=o=]], [[=(+)=]], and [o(+)] are completely equivalent.
[:character_class:]
Inside the brackets, between [: and :] is the name of the character class, which can represent all characters belonging to this class.
The names of character classes are: alnum, digit, punct, alpha, graph, space, blank, lower, upper, cntrl, print and xdigit
mysql> select "justalnums" regexp "[[:alnum:]] +"; -> 1 (indicates a match)
mysql> select "!!" regexp "[[:alnum:]]+"; -> 0 (indicates a mismatch)
[[::] ]
Matches an empty string at the beginning and end of a word respectively. Neither the beginning nor the end of the word is a character included in alnum and cannot be an underscore.
mysql> select "a word a" regexp "[[::]]"; -> 1 (indicates matching)
mysql> select "a xword a" regexp "[[::]]"; -> 0 (indicates no match)
mysql> select "weeknights" regexp "^(wee|week)(knights|nights)$"; -> 1 (indicates match)

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