Question

I have an issue with this mysql query. basically I need to join one table (CostiFissi, a table with costs) with a table with payments (Pagamenti), grouping them by cost id (CostiFissi_IdCostoFisso) and calculating the average between monthly sums of payments amount (not just AVG(Totale) ).

i.e.: the average between 1000+2000 on September and 3000 on October should return 2250 not 3000

this is what I did so far:

SELECT `cf`.`IdCostoFisso`, 
       `cf`.`Nome`, 
       `cf`.`Frequenza`, 
       `cf`.`Importo`, 
       `cf`.`DateFrom`, 
       `cf`.`DateTo`, 
        SUM( p.Totale ) PagamentiTotale, 
        COUNT( p.IdPagamento ) PagamentiNum, 
        AVG(p2.somma_mese) Media 
 FROM (`CostiFissi` cf) 
 LEFT JOIN `Pagamenti` p ON `p`.`CostiFissi_IdCostoFisso` = `cf`.`IdCostoFisso` 
 LEFT JOIN (
             SELECT MONTH(Data), 
                    YEAR(Data), 
                    CostiFissi_IdCostoFisso, 
                    SUM(Totale) somma_mese 
             FROM Pagamenti 
             GROUP BY YEAR(Data), 
                      MONTH(Data), 
                      CostiFissi_IdCostoFisso 
           ) AS p2 ON `p2`.`CostiFissi_IdCostoFisso` = `cf`.`IdCostoFisso` 
  WHERE `cf`.`DateTo` > '2012-09-27 09:46:14' 
         AND `p`.`Data` >= '2012-01-01 00:00:01' 
         AND `p`.`Data` <= '2012-12-31 23:59:59' 
  GROUP BY `cf`.`IdCostoFisso`

than when I run the query I get this issue: say I have 2 costs, cost_a (w/3 payments) and cost_b (w/1 payment), I get back the right mean for both (as I want it to be calculated) but COUNT( p.IdPagamento) returns 6 (and not 3) for cost_a and 1 for cost_b. the same for SUM (p.Totale), that’s doubled for cost_a and not for cost_b.

maybe is an issue with table p joining, dunno… it took a while for me to get to this point but now it’s a bit messy and I can’t get further >_<

ty!

Answer 1

Use COUNT(DISTINCT) like so:

COUNT(DISTINCT p.IdPagamento)

Instead of COUNT(p.IdPagamento).