Find in MySQL_ in_ Detailed explanation of set() function usage

1、 Official meaning （MySQL Grammar instructions in the manual ）

FIND_IN_SET(str,strlist), This function is used to query fields (strlist) Include in (str) Result , The return result is null Or record .

str String to query
strlist   Fields to query , Parameter with ”,” Separate , In the form of (1,2,6,8,10,22)
If the string str In by N A list of strings composed of sub chains strlist in , Then the return value range is 1 To N Between . A list of strings is a list of characters that are ‘,’ A string consisting of sub chains separated by symbols .

If the first parameter is a constant string , And the second is type SET Column , be FIND_IN_SET() Functions are optimized , Use bit calculation . If str be not in strlist or strlist Is an empty string , The return value is 0 . If any parameter is NULL, The return value is NULL. This function contains a comma in the first argument ( , ) Will not work properly .

Example ：

SELECT FIND_IN_SET('b', 'a,b,c,d');
//  result ：2
//  because  b  stay strlist Collection 2 The location of , a Is the position 1
 
select FIND_IN_SET('1', '1');
//  result ：1 
//  By this time strlist The set is a little special , There is only one string 
 
select FIND_IN_SET('2', '1,2'); 
//  result ：2
 
select FIND_IN_SET('6', '1'); 
//  result ：0 strlist Does not exist in the str, So back 0.

Sum up ： FIND_IN_SET Function , If the previous string is contained in the next string set , Return is greater than the 0 Number of numbers , This number is the position of the previous string in the next string .

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2、find_in_set() and in The difference between

New test table , Add several test data .

CREATE TABLE `test` (
  `ID` int(11) NOT NULL,
  `LIST` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
 
-- ----------------------------
-- Records of test
-- ----------------------------
INSERT INTO `test` VALUES ('1', 'AA,BB,CC');
INSERT INTO `test` VALUES ('2', 'AA,BB');
INSERT INTO `test` VALUES ('3', 'AA');

find_in_set() and in Query comparison of

-- IN Query field conditions 
SELECT id,list,' Field conditions ' AS 'IN Field ' from TEST WHERE list in ('AA');
 
-- IN Query constant conditions - Condition is true 
SELECT id,list,' Condition is true ' AS 'IN Constant condition is true ' from TEST WHERE 'AA' in ('AA','BB');
 
-- IN Query constant conditions - The condition is false 
SELECT id,list,' The condition is false ' AS 'IN Constant condition is false '  from TEST WHERE 'AA' in ('BB','CC');
 
-- FIND_IN_SET Field conditions 
SELECT id,list,' Field conditions ' AS 'FIND_IN_SET Field ' from TEST WHERE FIND_IN_SET('AA', list);
 
-- FIND_IN_SET Constant condition is true 
SELECT id,list,' Condition is true ' AS 'FIND_IN_SET Constant condition is true ' from TEST WHERE FIND_IN_SET('AA', 'AA,BB,CC');
 
-- FIND_IN_SET Constant condition is false 
SELECT id,list,' The condition is false ' AS 'FIND_IN_SET Constant condition is false ' from TEST WHERE FIND_IN_SET('AA', 'BB,CC');

  difference ：

1、in It can only be followed by a constant , find_in_set() Functions can use constants or fields .

2、in It's a perfect match ,find_in_set() Functions are exact matches , Field values are in English ”,” Separate .

another ：like Is a wide range of fuzzy matching , There is no delimiter in the string ,Find_IN_SET It's an exact match , Field values are in English ”,” Separate ,Find_IN_SET The result of the query should be less than like Result of query .

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3、 Application scenarios

1、 Article table type A field

There is a type Field , It stores article types , Yes 1 headlines 、2 recommend 、3 hotspot 、4 Graphics and so on . Now there's an article where he's the headline , It's hot again , Or graphics ,type China and Israel 1,3,4 Format store . So how do we use sql Find all type There is 4 What about the graphic type of articles ？

select * from article where FIND_IN_SET('4',type)

2、 Department tree query , Match the current node and all child nodes

Data table field description

  Matching Department id Or the father id by 100 The data of

SELECT dept_id FROM sys_dept WHERE dept_id = 100 or FIND_IN_SET( 100 , ancestors )