Question

How to remove duplicate records with merging values?

I have the table with id (integer pm key), val1 (text), val2 (text).

Current situation:

------------------

 id  val1    val2

 1.  john     sam
 2.  larry    tom
 3.  john     joe

I want to have:

---------------

 id  val1    val2

 1.  john     sam, joe
 2.  larry    tom
...

Thank you very much for your help.

Answer 1

As far as I know, you can’t do this, you can’t UPDATE and DELETE in one single query. However, you can do this as two UPDATE and DELETE queries like so:

UPDATE Table1 t1
INNER JOIN
(
  SELECT val1, GROUP_CONCAT(val2 SEPARATOR ',') Val2
  FROM Table1
  GROUP BY val1
) t2 ON t1.val1 = t2.val1
SET t1.val2 = t2.val2;

DELETE t
FROM table1 t
WHERE id NOT IN
(
  SELECT ID
  FROM
  (
    SELECT MIN(ID) id, val1
    FROM table1
    GROUP BY val1
   ) sub
 );

This will make the changes you want.

Note that: You have to put these two queries in one TRANSACTION.

SQL Fiddle Demo

These two queries will make your table looks like:

| ID |  VAL1 |    VAL2 |
------------------------
|  1 |  john | sam,joe |
|  2 | larry |     tom |