SubQuery

Hi All,

I have a query which is as follows

Select COL1,COL2,COL3
(SELECT MAX(COST)
FROM COSTTABLE
WHERE COSTTABLE.NO = SALESTABLE.NO) SALESCOST
FROM Materials INNER JOIN
PROJECTS ON MATERIALS.NO = PROJECTS.NO

My problem is I am getting 2 similar rows for Maxium cost,please can anyone let me know how can I select single row.I have COSTID WHICH IS IDENTITY COLUMN ,I am not sure how to select the max costid ......Please anyone .......can let me know