Detailed explanation of regular expression (regexp) in MySQL

Catalog

Preface

LIKE and REGEXP The difference between

OR Match

Match range

Match special character

Match character class

Match multiple instances

Locator

^ There are two uses

attach ：Mysql String interception and Intercept characters for query

summary

Preface

Sometimes use MySQL When querying data in the database ,like Query has limitations , It can be used at this time MySQL The way of regular expression query in .

Regular expressions are special strings used to match text （ Character set ）, Put a pattern （ Regular expressions ） Compare with a text string .

Extract phone numbers from text files

Find a file with a number in the middle of its name

Repeated words in the text block

Replace page URL For these URL Actual link to ( One or two regular expressions )

LIKE and REGEXP The difference between

LIKE Match the entire column （like It's fuzzy query ）, If the matched text appears only in the column value ,LIKE Will not find it , The corresponding line will not return （ Of course , Use wildcards except ）
REGEXP Match within column values , If the matched text appears in the column value ,REGEXP It will be found , The corresponding line is returned , At this time, a very important difference （ Of course , If you adapt to positioning symbols ^ and $, Can achieve REGEXP Match the entire column instead of a subset of the column ）

for example ：

Query a table name The column contains chen String data , Two article sql The statement is as follows

select * from stu_info where name like ' The small white ';select * from stu_info where name regexp ' The small white ';

The first query result is name The value is equal to ’ The small white ‘ The data of , The second query result is name Contained in the ’ The small white ’ The data of , It can also be used. like（ Fuzzy query + wildcard ） To achieve regexp Query results .

OR Match select column from table where column regexp 'X|Y' order by column;select column from table where column regexp '[XY]test' order by column;

The first way of writing will be | Apply to the whole string , As long as there is X or Y The data of , Will be retrieved

The second way of writing only [XY] Apply to the beginning of the search pattern

Match range

([]) A set can be used to define one or more characters to match , such as [0123456789], To simplify this type of collection , You can use （-） To define a range , namely [0-9],[a-z]

Match special character

Then the expression is composed of special characters with specific meanings ; If you want to match these special characters , It needs to be used. \ As the leader , This treatment is called escape （escaping）, All characters with special meaning in regular expressions must be escaped in this way ;（ To match the backslash {} Character itself , Need to use \\）

Be careful ： Most regular expression implementations use a single backslash to escape special characters , So that these characters themselves can be used , and MySQL Two backslashes are required （MySQL Explain one for yourself , The regular expression library interprets a ）

Match character class

Sometimes we need to retrieve the numbers we need 、 Matching of all alphabetic characters or all alphanumeric characters, etc , We can use predefined character sets , Called character class .

Match multiple instances

Sometimes it is necessary to have more control over the number of matches , such as ： Find all the numbers , No matter how many numbers are included in the number , Or find a word and follow it s（ If there is ） , etc. , We can use repeated metacharacters in regular expressions to complete .

select column from table where column regexp '\\([0-9] sticks?\\)' order by column;

The above regular expression ‘\([0-9] sticks?\)’ Meaning for ：\ matching （[0-9] Match any number , This refers to the range of matching values ,sticks? matching stick and sticks{? send s Optional , because ？ Match any character before it 0 perhaps 1 time }）.

Locator

Sometimes in order to match the text in a specific position , Need to use locator , The list of commonly used locators is as follows ：

Find one by one （ Including the number starting from the decimal point ） All values at the beginning , Simple search [0-9\.] or （[[:digit:]\.]） no way , Because it will find a match anywhere in the text , have access to ^ Locator , as follows ：

select column from table where column regexp '^[0-9\\.]' order by column;^ There are two uses

In the assembly （ use [ and ] Definition ）, Use it to negate the set

Used of the beginning of a string

send regexp and like Do the same thing ：like Match whole string two regexp Match the strings , You can use locators , use ^ Start each expression , use $ End each expression , You can make regexp and like It works the same .

Inquire about admin In the table group Field , The data format is ：1,2,3;4,5,6;1,87,101

For example, query 101：

select * from xin_admin where `group` REGEXP '[,|;]?101[,|;]?'; attach ：Mysql String interception and Intercept characters for query

One 、MySQL Interception of strings in

MySQL There is a special string interception function in ： There are two commonly used ：substring_index(str,delim,count) and concat

1.substring_index(str,delim,count) Functions are commonly used .

The functions in parentheses are ： To separate the intercepted string （ Such as ：”aaa_bbb_ccc”）、 Separator （ Such as ：“_”）、 Location （ Indicates the number of separators , Such as ：“1”）.

count Is a positive number , Then count from the left , Function returns the second count String to the left of separator ;

count It's a negative number , So it's counting from the right , Function returns the second count Everything to the right of the separator ;

count It can be for 0, Return to empty .

Example ：substring_index("aaa_bbb_ccc","_",1) , Return to aaa;
         substring_index("aaa_bbb_ccc","_",2) , Return to aaa_bbb;
         substring_index(substring_index("aaa_bbb_ccc","_",-2),"_",1) , Return to bbb;

2.concat Is to connect several strings

Example ：concat(‘m’,’y’,’s’,’q’,’l’);

return ：mysql

Two 、 Query all data containing this character according to a field in the table

1.find_in_set：SELECT * FROM user WHERE find_in_set(‘ Wu ’,name);

Inquire about user All in the table name contain “ Wu ” The data of

2.REGEXP：SELECT * FROM user WHERE name REGEXP ‘(‘ Wu ’|‘ Liu ’)’;

Use regular , Query data containing Liu or Wu

summary

This is about MySQL Regular expressions in (REGEXP) This is the end of the article , More about MySQL For regular expression content, please search the previous articles on SDN or continue to browse the following related articles. I hope you can support SDN in the future ！