MySQL - SUM(GROUP BY)?

I'm having an issue where I need to get the sum of a group of values in a select statement,. Basically, I need to:

  SELECT col1, col2, SUM(col2) AS col3 
    FROM myTable 
GROUP BY col1

where col1 will wind up into about 3 groups and col2 contains around 40 values... so I don't need col3 to be the same value [the sum of col2] but the sum for col2 for each group of col1

* EDIT * ok - here is the actual query:

select a.id,a.alloyname,a.label,a.symbol, g.grade, 
    if(a.id = 1,(
        ((( select avg(cost/2204.6) as averag开发者_如何学PythoneCost 
            from nas_cost where cost != '0' 
            and `date` >= '#variables.firstOfMonth#' 
            and `date` <= '#variables.lastOfMonth#') - t.value) * (astm.astm/100) * 1.2)),
        if(a.id = 2,(
            ((ep.estPrice - t.value) * (astm.astm/100) * 1.2)),
        if(a.id = 3 or a.id = 4 or a.id = 6 or a.id = 7,(
            ((ep.estPrice - t.value) * (astm.astm/100) * 0.012)),
        if(a.id = 5,(
            ((ep.estPrice - t.value)/2240 * (astm.astm/100))),
        if(a.id = 8,(
            if(((ep.estPrice - t.value)* (astm.astm/100)) >= 0,((ep.estPrice - t.value)* (astm.astm/100)), 0)),
    0)))))
    as thisValue

from nas_alloys a 
left join nas_triggers t on t.alloyid = a.id
left join nas_astm astm on astm.alloyid = a.id
left join nas_estimatedprice ep on ep.alloyid = a.id
left join nas_grades g on g.id = astm.gradeid
order by g.grade;

I need the total of 'thisValue' grouped by grade... trying to get my head around it..

You can use a subquery for this

SELECT col1, col2, (
    select SUM(col2)
    from mytable A
    where A.col1 = myTable.col1) as col3
FROM myTable

ANSI-92 Format:

   SELECT a.col1, 
          a.col2, 
          COALESCE(b.col3, 0) AS col3
     FROM YOUR_TABLE a
LEFT JOIN (SELECT t.col1,
                  SUM(t.col2) AS col3
             FROM YOUR_TABLE t
         GROUP BY t.col1) b ON b.col1 = a.col1

The LEFT JOIN will return NULL when there's no supporting col1 reference -- COALESCE will convert those situations into zero in this example

ANSI-89 Format

SELECT a.col1, 
       a.col2, 
       (SELECT SUM(b.col2)
                   FROM YOUR_TABLE b
                  WHERE b.col1 = a.col1) AS col3
  FROM YOUR_TABLE a

This will return NULL when there's no supporting col1 reference in the subquery.