在sum-sqlserver中嵌套Case语句

对此有问题:

我有下面的问题,给了我确切的看法,我需要。

SELECT t.Week,
       SUM(t.Hours) AS AH,
       SUM(c.Input) AS input,
       SUM(c.[recruitedPos]) AS recruitedPos,
       (SUM(t.Hours) - SUM(c.Input)) AS Possible
FROM tempPOC AS t
     LEFT JOIN (SELECT Week,
                       SUM(input) AS Input,
                       SUM([Normal Weekly Hours]) AS recruitedPos,
                       Shop
                FROM colData
                GROUP BY week,
                         Shop) AS c ON t.Week = c.Week
                                   AND c.Shop = t.Store
GROUP BY t.Week,
         t.Store
ORDER BY t.Week;

我遇到的问题是编写一个case语句,如果值小于0,则将可能的alias中的任何值设置为0。

(CASE(SUM(t.Hours - c.Hours)) < 0 then 0 else Possible end as Possible)

但这给了我一个错误

消息156,15级,状态1,第9行

Week, AH, Input, RecruitedPos, Possible
1,    15, 25,    13,            -10
1,    30, 15,    15,            15

预期产量:

Week, AH, Input, RecruitedPos, Possible
1,    15, 25,    13,            0  
1,    30, 15,    15,            15