Sum of calculated field

Question

I have two tables:

• table1 (a,b,c)
• table2 (a,d,f)

I want to get for each b to get sum of multiplication of corresponding d and f

table 1 data

a   b      c
-------------
1   hello  3
2   bye    4

table 2 data

a  d  f
--------
1  5  3
1  2  4
2  1  3
2  2  3

result: hello:5*3+2*4 , bye:1*3+2*3
My query is:

  SELECT t1.a, 
         t2.d * t2.f AS m, 
         SUM(m)   
    FROM table1 AS t1, 
         table2 AS t2 
   WHERE t1.a = t2.a 
GROUP BY t1.b

So what is wrong here? In mysql I get #1054 - Unknown column 'm' in 'field list'

Answer 1

Try:

SELECT t1.a, t2.d*t2.f AS m, SUM(t2.d*t2.f)
FROM table1 AS t1, table2 AS t2 
WHERE t1.a=t2.a GROUP BY t1.b

(I.e. expand the alias)