MySQL function GROUP_CONCAT

Turn - https://www.cnblogs.com/mytzq/p/7090193.html

This function returns the string with a non-NULL value results from the connection of one group. This function is an enhanced Sybase SQL Anywhere supports the basic LIST () function.

Grammatical structures:

 
          GROUP_CONCAT([ 
          DISTINCT 
          ] expr [,expr ...] [ 
          ORDER  
          BY  
          {unsigned_integer | col_name | expr} [ 
          ASC  
          |  
          DESC 
          ] [,col_name ...]] [SEPARATOR str_val])

DISTINCT: removing duplicate values

expr [, expr ...]: one or more fields (or expressions)

ORDER BY {unsigned_integer | col_name | expr} [ASC | DESC] [, col_name ...]: sorted according field or expression may be a plurality of

SEPARATOR str_val: separator (default comma)

Example 1: Query a classification of all sub-categories and sub-categories connection ID with a comma

 
          mysql> 
          SELECT  
          GROUP_CONCAT(cat_id)  
          FROM  
          goods_cat  
          WHERE  
          pid = 25 
         
          + 
          -----------------------------+ 
         
          | GROUP_CONCAT(cat_id)        | 
         
          + 
          -----------------------------+ 
         
          | 26,111,130,206,239,322,323  | 
         
          + 
          -----------------------------+

Example 2: Search for a child of sorting and classification ID linker with a semicolon

 
          mysql> 
          SELECT  
          GROUP_CONCAT(cat_id SEPARATOR  
          ';' 
          )  
          FROM  
          goods_cat  
          WHERE  
          pid = 25 
         
          + 
          -------------------------------------+ 
         
          | GROUP_CONCAT(cat_id SEPARATOR  
          ';' 
          )  | 
         
          + 
          -------------------------------------+ 
         
          | 26;111;130;206;239;322;323          | 
         
          + 
          -------------------------------------+

Example 3: Query a classification of all sub-categories, according to the connection p_order ASC, cat_id DESC after sorting

 
     
      
        
          mysql> 
          SELECT  
          GROUP_CONCAT(cat_id  
          ORDER  
          BY  
          p_order  
          ASC 
          , cat_id  
          DESC 
          )  
          FROM  
          goods_cat  
          WHERE  
          pid = 25 
         
 
          + 
          ----------------------------------------------------------+ 
         
 
          | GROUP_CONCAT(cat_id  
          ORDER  
          BY  
          p_order  
          ASC 
          , cat_id  
          DESC 
          )   | 
         
 
          + 
          ----------------------------------------------------------+ 
         
 
          | 332,331,242,212,133,112,29,26,333,330,327,244,138,116    | 
         
 
          + 
          ----------------------------------------------------------+ 
         
 
      
 
     
   

Example 4: combined GROUP BY query

 
          mysql> 
          SELECT  
          pid, GROUP_CONCAT(cat_id)  
          FROM  
          goods_cat  
          GROUP  
          BY  
          pid 
         
          + 
          -----------+-------------------------------------+ 
         
          | parent_id | GROUP_CONCAT(cat_id)                | 
         
          + 
          -----------+-------------------------------------+ 
         
          |        22 | 35,166,191,209,233,252,256,257,258  | 
         
          |        25 | 26,111,130,206,239,322,323          | 
         
          |        26 | 29,51,65,66,70,75,238               | 
         
          |       323 | 332,333,334,335,336,337,338,339     | 
         
          + 
          -----------+-------------------------------------+

note:

1. Maximum length (characters) limits

System variables: group_concat_max_len

 
          SET  
          [SESSION |  
          GLOBAL 
          ] group_concat_max_len = val;

val must be an unsigned integer

GROUP_CONCAT with the function, SELECT statement LIMIT statement no role to play.

2. INT type trap

When connected to INT field type, version, or low results are not returned string comma-delimited occurs, but byte [].

In this case, the need for conversion CAST or CONVERT function.