MySQL: How to update SUM() values of children to a parent row in the same table?

Question

I need to get the sum values of my child rows and update that data on the parent row. I've got this for as shown below but ran into error #1111 (Invalid use of group function).

CREATE TEMPORARY TABLE cms_ladu_temp LIKE cms_ladu;

INSERT INTO cms_ladu_temp SELECT * FROM cms_ladu WHERE parent_id IN (326,500);

UPDATE 
    cms_ladu 
INNER JOIN
    cms_ladu_temp
ON
    cms_ladu_temp.parent_id=cms_ladu.id 
SET  
    cms_ladu.child_packaging_units_in=SUM(cms_ladu_temp.packaging_units_in), 
    cms_ladu.child_net_weight_in=SUM(cms_ladu_temp.net_weight_in) 
WHERE 
    cms_ladu.id IN (326,500);

Answer 1

What you need to do is group by the id to separate the child sums for each parent id. You will need to use a subselect to accomplish this.

Also, you don't need to create a temporary table. Just wrap the aggregation in a subselect (grouping by parent_id), and join the subselect onto the main table:

UPDATE 
    cms_ladu a
INNER JOIN
(
    SELECT   parent_id, 
             SUM(packaging_units_in) AS pui,
             SUM(net_weight_in) AS nwi
    FROM     cms_ladu
    WHERE    parent_id IN (326,500)
    GROUP BY parent_id
) b ON a.id = b.parent_id
SET 
    a.child_packaging_units_in = b.pui,
    a.child_net_weight_in = b.nwi