Summary on the use of REGEXP regular expressions in MySQL

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）

Related recommendations:

JS regular expression perfectly realizes the ID card verification function

How to use regular expressions to highlight JavaScript code

javascript matches the regular expression code commented in js

The above is the detailed content of Summary on the use of REGEXP regular expressions in MySQL. For more information, please follow other related articles on the PHP Chinese website!