Text processing function sorting in mysql, quick search of collection

Hello everyone , I'm Xiangyu ！

Preface

​ I've arranged for a while today MySQL Text processing function in , Of course, if Xiangyu arranges and misses the message on the backstage . No matter in which programming language , The processing of text is extremely important , Because everyone knows , In daily data , Texts will account for a large part , therefore , The bosses directly encapsulate the commonly used processing operations , In this way, you don't need to write your own functions when processing text , And in fact, it also gives a friendly feeling to many new friends , For example, many data analysts

Study SQL Just want to take a number , It's not a view to learn at all 、 stored procedure 、 function , So at this point , If you can use encapsulated built-in functions directly , That's the gospel of my friends , Said so much , That is to say, text processing functions are very important , Of course , Xiangyu has tidied up here , You can collect , When you need it, just check it quickly , Don't bother, you can also try to tidy up like Xiangyu .

1. Mind mapping

2. Using examples

The following example does not specifically look up the table , Direct use select To test .

2.1 Interception and splicing

left： Left hand intercept , From the front （ On the left ） Intercept a certain length of substring for the string backwards , grammar ：left（ character string , Interception length ）

select left(' The Yangtze River flows east ',4);    --  return “ Rolling Yangtze River ”

right： Right intercept , From the back （ On the right ） Truncate a certain length of substring to the string forward , grammar ：right（ character string , Interception length ）

select right(' The Yangtze River flows east ',4);    --  return “ The east of the river is flowing ”

substring ： Intercept the substring with specified position and length for the string , grammar ：substring（ character string , From the first few characters [, Interception length ]）

Be careful ： The grammatical [] Indicates that this parameter can be defaulted

The third parameter of this function can be defaulted （ No ）, By default, it means to intercept the last character

select substring(' Rolling Yangtze River board ',3);   --  return “ Changjiang board of directors ”

select substring(' The rolling Yangtze River is full of water ',3,2);  --  return “ Yangtze River ”

concat： String splicing , grammar ：concat（ character string 1[, character string 2, character string 3,…]）

The parameters of this function can be given to one or more , When the parameter has null when , The result also returns null

select concat(' Rolling ')  --  return  “ Rolling ”

select concat(' Rolling ',null)  -- return  null

select concat(' Rolling ',' Yangtze River ',' East death ',' water ')   --  return  “ The Yangtze River flows east ”

2.2 transformation

lower： Convert to lowercase , grammar ：lower（ String to be converted ）

select lower('HELLO,WORLD');  --  return  “hello,world”

upper ： Convert to uppercase , grammar ：upper（ String to be converted ）

select upper('hello,world');   --  return  "HELLO,WORLD"

2.3 length

length ： Returns the length of the string , grammar ：length( character string )

select length(' The Yangtze River flows east ');   --  return 21（ One Chinese character takes up the length of three English characters ）

select length('hello');      --  return 5

select length(null)          --  return null

2.4 Find the substring position

locate： When a substring can be found in the original string, its first position in the original string is returned , grammar Locate（ Substring , Parent string ）

explain ： The substring does not exist and returns 0, The substring is null return null

select locate('sql',' Xiangyu is learning mysql Or what kind sql');   --  return 8, first s Is the eighth character 

select locate('pgsql',' Xiangyu is learning mysql Or what kind sql');   --  return 0

select locate(null,' Xiangyu is learning mysql Or what kind sql');    --  return null

position ： and locate Function as , The writing is different , grammar position（substr in str）

select position('sql' in ' Xiangyu is learning mysql Or what kind sql');   --  return 8

instr： The function is the same as the previous two , The writing is different , grammar ：instr（str,substr）

select instr(' Xiangyu is learning mysql Or what kind sql','sql');   --  return 8

2.5 Go to space

ltrim： Remove the leading space in the string , Is to remove the blank space at the beginning , grammar ：ltrim（ character string ）

select ltrim('  It's early morning 2 spot  ');     --  return “ It's early morning 2 spot  ”

rtrim： Remove trailing space from string , grammar ：rtrim（ character string ）

select rtrim('  It's two in the morning  ');    --  return “  It's two in the morning ”

trim： Remove leading and ending spaces in the string , But it can't remove the space in the middle , grammar ：trim（ character string ）

select trim('  Now it is   In the morning   At two o 'clock  ');  --  return  “ Now it is   In the morning   At two o 'clock ”

2.6 fill

lpad： Returns a fixed length string , Interception beyond a fixed length , Below the fixed length, use the specified characters Left fill , grammar ：lpad（ character string , Fixed length , The characters that need to be filled in ）

Below the fixed length

select lpad(' One gao Nest gaogao',20,'*');     --  return  "******** One gao Nest gaogao"

When the fixed length is exceeded

select lpad(' Frenchman Zhang San ',4,'^^');  --  return “ Outlaw maniac ”

rpad： Returns a fixed length string , Interception beyond a fixed length , Below the fixed length, use the specified characters Right fill , grammar ：rpad（ character string , Fixed length , The characters that need to be filled in ）

Below the fixed length

select rpad(' One gao Nest gaogao',20,'*');     --  return  " One gao Nest gaogao********"

When the fixed length is exceeded

select rpad(' Frenchman Zhang San ',4,'^^');  --  return “ Outlaw maniac ”

2.7 Replace

replace： Replace the substring in the string with a new substring and return , grammar ：replace（ Original string , Substring to be replaced , Substring for replacement ）

select replace(' The Yangtze River flows east ',' roll ',' Don't get out ');   --  return “ Don't roll, don't roll, the Yangtze River flows eastward ”

Be careful ： It will be completely replaced when replacing , It is not allowed to set the substring that meets the conditions

2.8 Return to pronunciation

soundex： Returns the phonetic representation of a string soundex, It helps to compare words with different spelling but similar English pronunciation , grammar ：soundex（ character string ）

for example ：

If a file named Y.LEE Wrong input when searching for customers , Below sql There will be no return results .

SELECT CUSTOMER_NAME FROM CUSTOMER WHERE CUSTOMER_NAME = 'Y LEE'

And if you write that ：

SELECT CUSTOMER_NAME FROM CUSTOMER WHERE SOUNDEX(CUSTOMER_NAME) =SOUNDEX('Y LEE')

Because they sound similar , So their SOUNDEX Values match , This will return a piece of data .

soundex Refer to ：https://www.cnblogs.com/shuoli/p/8099212.html

Okay ,sql The text function of is summarized here , Welcome to pay attention to add collection , At the same time, you are also welcome to Xiangyu's official account of the same name , Xiangyu is constantly updating !