Question

Ok, I have a query over two tables. I need to get two sums. I do a group by so the sum() works correctly.

SELECT sum(a.x), sum(b.y) FROM a,b GROUP BY a.n where a.n=b.m

So far this works well, but the problem is i need to group them differently for the second sum (sum(b.y)), than for the first sum (sum(a.x)).

The real query is somewhat more complex but this is my main problem.

This is what i actually try to select sum(stock.amount) - if( sold.amount IS NULL , 0, sum( sold.amount ) )

How can I solve that in one query?

Answer 1

since you are not writing down the tables I am gonna make a wild guess and assume the tables are like :

stock : id, item_id, amount
sold : id, item_id, amount

then again I assume that you need the stock_in_total, sold_total, left_total counts

SELECT 
  stock_sums.item_id, 
  stock_sums.st_sum as stock_in_total,
  COALESCE(sold_sums.so_sum,0) as sold_total,
  (stock_sums.st_sum - COALESCE(sold_sums.so_sum,0)) as left_total
FROM (
  SELECT stock.item_id as item_id, SUM(stock.amount) as st_sum 
  FROM stock 
  GROUP BY item_id
) as stock_sums 
LEFT JOIN (
  SELECT sold.item_id as item_id, SUM(sold.amount) as so_sum 
  FROM sold
  GROUP by item_id
) as sold_sums ON stock_sums.item_id = sold_sums.item_id

I hope this would help.