MySQL未知列在where子句中，但该列存在

Question

So it seems some people have had this problem before, but searching didn't turn up an answer for my case.

I'm running

 UPDATE ProdCosts SET PercentCost = ((ProdCosts.PieceCost/totalprodcost.sumpiececost)*100)
 WHERE totalprodcost.ProdNo=ProdCosts.ProdNo;
 AND ProdCosts.PieceCost > 0;

and getting the error

MySQL said: Documentation
#1054 - Unknown column 'totalprodcost.ProdNo' in 'where clause' 

DESCRIBE totalprodcost shows:

Field   Type    Null    Key     Default     Extra
ProdNo  int(11) YES         NULL    
sumpiececost    double  YES         NULL    

I can't figure this out. It seems simple enough. What gives?

Answer 1

Join the tables on UPDATE statement,

UPDATE  ProdCosts a
        INNER JOIN totalprodcost b
            ON b.ProdNo = a.ProdNo
SET     a.PercentCost = ((a.PieceCost/b.sumpiececost)*100)
WHERE   a.PieceCost > 0;

Answer 2

Try this query

UPDATE ProdCosts, totalprodcost SET ProdCosts.PercentCost = ((ProdCosts.PieceCost/totalprodcost.sumpiececost)*100) WHERE totalprodcost.ProdNo=ProdCosts.ProdNo AND ProdCosts.PieceCost > 0;