Sorry, forgot to add the group by statement so it should be like this:
Select a.Project_PK , SUM(b.cost) AS Sum_of_Cost , SUM(b.estimate_cost) AS Sum_of_Estimated_Cost , SUM(c.quantity) AS Sum_of_Quantity , SUM(c.estimate_quantity) AS Sum_of_Estimated_Quantity FROM Projects a LEFT JOIN Cost b ON a.project_pk = b.project_pk LEFT JOIN Quantity c ON a.project_pk = c.project_pk GROUP BY a.Project_PK -- Dixon Epperson
