选择CASE THEN

Question

我需要选择生效日期少于今天的项目费率或班次率。

 SELECT 
 CASE 
    WHEN ISNULL(s.rate,0) = 0 
    THEN SELECT TOP 1 pr.rate FROM ProjectRates pr WHERE (pr.projectID = p.ID) AND (pr.effectiveDate < GETDATE()) ORDER BY pr.effectiveDate DESC
    --p.rate 
    ELSE SELECT TOP 1 sr.rate FROM ShiftRates sr WHERE (sr.shiftID = s.ID) AND (sr.effectiveDate < GETDATE()) ORDER BY pr.effectiveDate DESC                
    --s.rate 
END AS rate
FROM Projects p
INNER JOIN Shifts s ON (p.ID = s.projectID)
WHERE (p.ID = @projectID)

请注意，此代码段是较大存储过程的一部分，因此必须在CASE语句中。

Answer 1

子查询需要括号：

SELECT (CASE WHEN ISNULL(s.rate, 0) = 0 
             THEN (SELECT TOP 1 pr.rate
                   FROM ProjectRates pr
                   WHERE (pr.projectID = p.ID) AND (pr.effectiveDate < GETDATE())
                   ORDER BY pr.effectiveDate DESC
                  )
             ELSE (SELECT TOP 1 sr.rate
                   FROM ShiftRates sr
                   WHERE (sr.shiftID = s.ID) AND (sr.effectiveDate < GETDATE()) 
                   ORDER BY pr.effectiveDate DESC                
                  ) --s.rate 
        END) AS rate
FROM Projects p INNER JOIN
     Shifts s 
     ON p.ID = s.projectID
WHERE p.ID = @projectID;