MySQL GROUP_CONCAT with COLUMN SPLIT

问题

I am working with a TABLE, need logical help.

Check the below URL for the table structure and sample data.

http://sqlfiddle.com/#!2/ece06/2

Table Schema:

CREATE TABLE test (
  ID INTEGER,
  NAME VARCHAR (50),
  VALUE INTEGER
);

Inserted Data:

INSERT INTO test VALUES (1, 'A', 4);
INSERT INTO test VALUES (1, 'B', 5);
INSERT INTO test VALUES (1, 'C', 8);
INSERT INTO test VALUES (2, 'D', 9);
INSERT INTO test VALUES (2, 'E', 9);
INSERT INTO test VALUES (3, 'F', 9);
INSERT INTO test VALUES (3, 'G', 9);
INSERT INTO test VALUES (3, 'H', 9);
INSERT INTO test VALUES (3, 'I', 9);

Query:

SELECT ID, GROUP_CONCAT(NAME) AS CODE
FROM test
GROUP BY ID;

OutPUT:

ID  CODE
1   A,B,C
2   D,E
3   F,G,H,I

Expected OUTPUT:

ID  CODE   CODE   CODE  CODE
1    A      B      C    NULL
2    D      E     NULL  NULL
3    F      G      H     I

As you can see the output of the query has concat with comma. And currently we are doing string concat using PHP which splits while displaying!!

Is there any other way to split the RESULT and show each value in column and same ROW? In same result?

Note: The CODE might vary for each ROW.

回答1:

If you know the number of GROUP_CONCAT entries(I mean 3 fields are combined in the case of ID =1 and 2 fields are combined in the case of 2 etc), then there is a dirty way.

SELECT ID, SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(NAME), ',', 1), ',', -1) AS CODE1,
If(  length(GROUP_CONCAT(NAME)) - length(replace(GROUP_CONCAT(NAME), ',', ''))>1,  
       SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(NAME), ',', 2), ',', -1) ,NULL) 
           as CODE2,
   SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(NAME), ',', 3), ',', -1) AS CODE3
FROM test
GROUP BY ID;

Output:

ID  CODE1   CODE2   CODE3
1   A          B    C
2   D       (null)  E
3   F          G    H

The above query assume that you are GROUP_CONCAT-ing 3 fields. If you are dynamically generating query you can give a try. SQLFIDDLE

EDIT: Note: The CODE might vary for each ROW.( Ignoring this)

回答2:

With Help from my colleague We arrived at a point to solve this senario. Hope some one might needed it.. It is welcome if some one make it much simpler.

BEGIN
SET @v=0;


SET @v1=0;


SELECT tmp.cnt INTO @v
FROM
  (SELECT Id,
          count(ID) AS cnt,
          GROUP_CONCAT(name)
   FROM test
   GROUP BY id) tmp
ORDER BY tmp.cnt DESC LIMIT 1;


SET @str=' ';

 WHILE(@v>@v1) DO
SET @v1=@v1+1;

 IF(@str='') THEN
SET @str=CONCAT(@str,'ID, REPLACE(SUBSTRING(SUBSTRING_INDEX(GROUP_CONCAT(NAME), '','',', @v1,'),LENGTH(SUBSTRING_INDEX(GROUP_CONCAT(NAME),'','',', @v1,'-1)) + 1),'','','''') AS Code' ,@v1);

 ELSE
SET @str= CONCAT(@str,',REPLACE(SUBSTRING(SUBSTRING_INDEX(GROUP_CONCAT(NAME),'','',', @v1,'),LENGTH(SUBSTRING_INDEX(GROUP_CONCAT(NAME),'','',' , @v1,' -1)) + 1),'','','''') AS Code',@v1);

 END IF;

 END WHILE;

SET @str=CONCAT('SELECT ' , @str, ' FROM test GROUP BY ID');

 PREPARE MYSQLQUERY
FROM @str;

 EXECUTE MYSQLQUERY;

 DEALLOCATE PREPARE MYSQLQUERY;

 END

回答3:

The only way to split that into columns will mean that you know the values you want to split in advance (eg: one column for codes matching A, D, F another one for B, E, G and so on). This doesn't seem to be the case.

The bullet proof approach would be not to group by and process the results in PHP.

The other possible way (not the one I would recommend) would be to change the saparator from a comma to something else. EG:

SELECT ID, GROUP_CONCAT(NAME SEPARATOR ';') AS CODE
FROM test
GROUP BY ID

回答4:

(SELECT ID, SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(NAME), ',', 1), ',', -1) AS CODE1,

If(  length(GROUP_CONCAT(NAME)) - length(replace(GROUP_CONCAT(NAME), ',', ''))>1,  

       SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(NAME), ',', 2), ',', -1) ,NULL)as CODE2,

   SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(NAME), ',', 3), ',', -1) AS CODE3,

       If(  length(GROUP_CONCAT(NAME)) - length(replace(GROUP_CONCAT(NAME), ',', ''))>2,  

       SUBSTRING_INDEX(SUBSTRING_INDEX(GROUP_CONCAT(NAME), ',', 4), ',', -1) ,NULL)as CODE4

FROM test
GROUP BY ID)

来源：https://stackoverflow.com/questions/20279781/mysql-group-concat-with-column-split

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php

mysql

sql

logic