Update mysql table based with group_concat

Question

UPDATE BELOW!

Who can help me out

I have a table:

CREATE TABLE `group_c` (
`parent_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`child_id` int(11) DEFAULT NULL,
`number` int(11) DEFAULT NULL,
  PRIMARY KEY (`parent_id`)
) ENGINE=InnoDB;


INSERT INTO group_c(parent_id,child_id)
VALUES (1,1),(2,2),(3,3),(4,1),(5,4),(6,4),(7,6),(8,1),(9,2),(10,1),(11,1),(12,1),(13,0);

I want to update the number field to 1 for each child that has multiple parents:

SELECT group_concat(parent_id), count(*) as c FROM group_c group by child_id having c>1

Result:

GROUP_CONCAT(PARENT_ID)     C
12,11,10,8,1,4          6
9,2                     2
6,5                     2

So all rows with parent_id 12,11,10,8,1,4,9,2,6,5 should be updated to number =1

I've tried something like:

UPDATE group_c SET number=1 WHERE FIND_IN_SET(parent_id, SELECT pid FROM (select group_concat(parent_id), count(*) as c FROM group_c group by child_id having c>1));

but that is not working.

How can I do this?

SQLFIDDLE: http://sqlfiddle.com/#!2/acb75/5

[edit]

I tried to make the example simple but the real thing is a bit more complicated since I'm grouping by multiple fields. Here is a new fiddle: http://sqlfiddle.com/#!2/7aed0/11

Answer 1

For anyone interested. This is how I solved it. It's in two queries but in my case it's not really an issue.

UPDATE group_c INNER JOIN (
SELECT parent_id, count( * ) AS c
FROM `group_c`
GROUP BY child1,child2
HAVING c >1
) AS cc ON cc.parent_id = group_c.parent_id
SET group_c.number =1 WHERE number =0;


UPDATE group_c INNER JOIN group_c as gc ON 
 (gc.child1=group_c.child1 AND gc.child2=group_c.child2 AND gc.number=1)
SET group_c.number=1;

fiddle: http://sqlfiddle.com/#!2/46d0b4/1/0

Answer 2

Why use GROUP_CONCAT() and then try to do something with it's result via FIND_IN_SET() ? That's not how SQL is intended to work. You may use simple JOIN to retrieve your records:

SELECT
  parent_id
FROM
  group_c
  INNER JOIN
  (SELECT 
    child_id, 
    count(*) as c 
  FROM 
    group_c 
  group by 
    child_id 
  having c>1) AS childs
  ON childs.child_id=group_c.child_id

-check your modified demo. If you want UPDATE, then just use:

UPDATE
  group_c
  INNER JOIN
  (SELECT 
    child_id, 
    count(*) as c 
  FROM 
    group_c 
  group by 
    child_id 
  having c>1) AS childs
  ON childs.child_id=group_c.child_id
SET
  group_c.number=1

Answer 3

Here's a similar solution...

UPDATE group_c a
  JOIN 
     ( SELECT DISTINCT x.child_id candidate
                  FROM group_c x
                  JOIN group_c y
                    ON y.child_id = x.child_id
                   AND y.parent_id < x.parent_id
     ) b
    ON b.candidate = a.child_id
   SET number = 1; 

http://sqlfiddle.com/#!2/bc532/1