In the past, I used like to find data. Later, I found that there are regular expressions in mysql and I feel that the performance is better than like. Now I will share with you a detailed explanation of the use of mysql REGEXP regular expressions. I hope this method will be helpful to everyone. .
Regular expression describes a set of strings. The simplest regular expression is one that does not contain any special characters. For example, the regular expression hello matches hello.
Non-trivial regular expressions adopt a special structure that allows them to match more than one string. For example, the regular expression hello|word matches the string hello or the string word.
As a more complex example, the regular expression B[an]*s matches any of the following strings: Bananas, Baaaaas, Bs, and any string starting with B, ending with s, and ending with Any other string containing any number of a or n characters.
The following are the schemas available for tables with the REGEXP operator.
Application example, find user records with incorrect email format in the user table:
SELECT *
FROM users
WHERE email NOT REGEXP '^[A-Z0-9._%-]+@[A-Z0-9.-]+.[A-Z]{2,4}$'Regular expression in MySQL database The grammar of formula mainly includes the meaning of various symbols.
(^) character
matches the starting position of the string, such as "^a" means a string starting with the letter a.
mysql> select 'xxxyyy' regexp '^xx'; +-----------------------+ | 'xxxyyy' regexp '^xx' | +-----------------------+ | 1 | +-----------------------+ 1 row in set (0.00 sec)
Query whether the xxxyyy string starts with xx. The result value is 1, which means the value is true and the condition is met.
($) character
matches the end position of the string, such as "X^" means a string ending with the letter X.
(.) Character
This character is the dot in English. It matches any character, including carriage return, line feed, etc.
(*) character
The asterisk matches 0 or more characters, and there must be content before it. For example:
mysql> select 'xxxyyy' regexp 'x*';
This SQL statement, the regular match is true.
(+) character
The plus sign matches 1 or more characters, and there must also be content before it. The plus sign is used similarly to the asterisk, except that the asterisk is allowed to appear 0 times, and the plus sign must appear at least once.
(?) character
question mark matches 0 or 1 times.
Example:
Now based on the above table, various types of SQL queries can be installed to meet the requirements. Here are some understandings. Consider we have a table as person_tbl and there is a field named name:
Query to find all names starting with 'st'
mysql> SELECT name FROM person_tbl WHERE name REGEXP '^st';
Query to find all The name ends with 'ok'
mysql> SELECT name FROM person_tbl WHERE name REGEXP 'ok$';
Query to find all the name strings containing 'mar'
mysql> SELECT name FROM person_tbl WHERE name REGEXP 'mar';
Query to find all names starting with a vowel and ending with 'ok'
mysql> SELECT name FROM person_tbl WHERE name REGEXP '^[aeiou]|ok$';
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（表示不匹配） mysql> select "fofo" REGEXP "^fo"; -> 1（表示匹配）
$
The matched string ends with the previous string
mysql> select "fono" REGEXP "^fono$"; -> 1（表示匹配） mysql> select "fono" REGEXP "^fo$"; -> 0（表示不匹配） .
Matches any character (including new lines)
mysql> select "fofo" REGEXP "^f.*"; -> 1（表示匹配） mysql> select "fonfo" REGEXP "^f.*"; -> 1（表示匹配）
a*
Match any number of a (including empty string)
mysql> select "Ban" REGEXP "^Ba*n"; -> 1（表示匹配） mysql> select "Baaan" REGEXP "^Ba*n"; -> 1（表示匹配） mysql> select "Bn" REGEXP "^Ba*n"; -> 1（表示匹配）
a+
Match any number of a (excluding empty string)
mysql> select "Ban" REGEXP "^Ba+n"; -> 1（表示匹配） mysql> select "Bn" REGEXP "^Ba+n"; -> 0（表示不匹配）
a?
Matches one or zero a
mysql> select "Bn" REGEXP "^Ba?n"; -> 1（表示匹配） mysql> select "Ban" REGEXP "^Ba?n"; -> 1（表示匹配） mysql> select "Baan" REGEXP "^Ba?n"; -> 0（表示不匹配）
de|abc
matches de or abc
mysql> select "pi" REGEXP "pi|apa"; -> 1（表示匹配） mysql> select "axe" REGEXP "pi|apa"; -> 0（表示不匹配） mysql> select "apa" REGEXP "pi|apa"; -> 1（表示匹配） mysql> select "apa" REGEXP "^(pi|apa)$"; -> 1（表示匹配） mysql> select "pi" REGEXP "^(pi|apa)$"; -> 1（表示匹配） mysql> select "pix" REGEXP "^(pi|apa)$"; -> 0（表示不匹配）
(abc)*
Match any number of abc (including empty string)
mysql> select "pi" REGEXP "^(pi)*$"; -> 1（表示匹配） mysql> select "pip" REGEXP "^(pi)*$"; -> 0（表示不匹配） mysql> select "pipi" REGEXP "^(pi)*$"; -> 1（表示匹配）
{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 one integer parameter i in {}, followed by ", ", 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 that the character can only appear i times or more, j times The following (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 " "
"[", "]" must be used in pairs
mysql> select "aXbc" REGEXP "[a-dXYZ]"; -> 1（表示匹配） mysql> select "aXbc" REGEXP "^[a-dXYZ]$"; -> 0（表示不匹配） mysql> select "aXbc" REGEXP "^[a-dXYZ]+$"; -> 1（表示匹配） mysql> select "aXbc" REGEXP "^[^a-dXYZ]+$"; -> 0（表示不匹配） mysql> select "gheis" REGEXP "^[^a-dXYZ]+$"; -> 1（表示匹配） mysql> select "gheisa" REGEXP "^[^a-dXYZ]+$"; -> 0（表示不匹配）
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