包含来自其他表中的列的两个总和的MySQL查询

Question

Got a query running one sum from a different table, which works perfectly (and obtained from this forum as well):

SELECT
    R.REP_ID as repid, R.REP_DESBREV as repdesc, 
    IFNULL(SUM(RD.REPDATA_CANT), 0) as cant
FROM 
    REPUESTOS R 
LEFT JOIN 
    REP_DATA RD, ON RD.REPDATA_REPID = R.REP_ID 
GROUP BY 
    RD.REPDATA_REPID

Now, the thing is that I'd like to add an extra column that obtains the total inventory (something like

IFNULL(SUM(I.INV_CANT), 0) as inv) 
FROM table INVENTARIO I
WHERE I.INV_REPID = R.REP_ID

This value can be obtained by means of a JOIN, in the exact same way we got the first statement that works, but I have not found the way to include BOTH SUMS in just one query.

Any ideas? THANKS!

Answer 1

Try this query example

select 
t1.id,
ifnull(sum(t1.my_column),0) as Sum1,
ifnull(other.sum,0) as Sum2
from table as t1
left join (select id , sum(other_table_column) from other_table group by id) as other
on t1.id = other.id
group by t1.id

Answer 2

I just implemented the following statement:

SELECT
    R.REP_PARNUM as parnum,
    R.REP_ID as repid,
    R.REP_DESBREV as repdesc,
    IFNULL(SUM(RD.REPDATA_CANT),0) as cant,
    IFNULL(SUM(I.INV_CANT),0) as intt
FROM REPUESTOS R
LEFT JOIN REP_DATA RD ON RD.REPDATA_REPID = R.REP_ID
LEFT JOIN INVENTARIO I ON I.INV_REPID = R.REP_ID
GROUP BY R.REP_PARNUM

It actually runs, but the problem is that it's giving me some weird values. For example, some of the values in the first sum column ( REPDATA_CANT ) are shown with -3, ie if the real result is 20, it shows 17 and so on. In the second sum column ( INV_CANT ), it actually MULTIPLIES (in some rows, not all) the value by 3. Very weird behaviour, do you have an idea why?