Invalid use of group function

**jimgym1989** · Mar 6 '10, 06:00 AM

Code:

select ABS(ROUND((projectspecs.laborCost+projectspecs.contingencyCost +
SUM(materialcost_details.qty*materialcost_details.unitCost))*
(billing.accom/100) - (projectspecs.laborCost+projectspecs.contingencyCost +
SUM(materialcost_details.qty*materialcost_details.unitCost))*
(billing.accom/100) * project.downpayment/100,2))
as billCost from project
LEFT JOIN billing ON project.project_id = billing.project_id
LEFT JOIN projectspecs ON projectspecs.project_id  = project.project_id
LEFT JOIN materialcost_details ON materialcost_details.psId = projectspecs.psID
where project.project_id = 120 group by(billing.billing_id) order by billing.billing_id

The result of this query is
billCost
1880.75
3684.78
1956.34
2443.74
1316.64

What I'm trying to do here is I want to get the SUM of the billCost and I'm doing this query

Code:

select ABS(ROUND(SUM((projectspecs.laborCost+projectspecs.contingencyCost +
SUM(materialcost_details.qty*materialcost_details.unitCost))*
(billing.accom/100) - (projectspecs.laborCost+projectspecs.contingencyCost +
SUM(materialcost_details.qty*materialcost_details.unitCost))*
(billing.accom/100) * project.downpayment/100),2))
as billCost from project
LEFT JOIN billing ON project.project_id = billing.project_id
LEFT JOIN projectspecs ON projectspecs.project_id  = project.project_id
LEFT JOIN materialcost_details ON materialcost_details.psId = projectspecs.psID
where project.project_id = 120 group by(billing.billing_id) order by billing.billing_id

it says that I have an Invalid use of group function
What's wrong with my query? I just want to get the SUM of billCost