Question

我的sql程序中有以下查询

SELECT
    m.managerid,
    CASE
        WHEN (ISNULL(COUNT(t.employeeid), 0) = 0) THEN 'No Manager'
        ELSE COUNT(m.managerid)
    END
FROM employee t
LEFT JOIN employenrol m
    ON t.employeeid = m.employeeid
GROUP BY t.employeeid

if count(t.employeeid)= 0我需要显示没有经理其他实际计数。

将varchar值'No Manager'转换为时转换失败数据类型int。警告：聚合或消除空值其他SET操作。

如何解决这个问题？

Answer 1

来自MSDN

else_result_expression和任何result_expression的数据类型必须是相同的或必须是隐式转换。

您需要在else部分中进行显式转换，因为第一个then语句返回VARCHAR，无法转换为INT。

SELECT t.employeeid, 
       CASE 
         WHEN Count(m.employeeid) = 0 THEN 'No Manager' 
         ELSE Cast(Count(m.employeeid) AS VARCHAR(50)) 
       END 
FROM   employee t 
       LEFT JOIN employenrol m 
              ON t.employeeid = m.employeeid 
GROUP  BY t.employeeid

如果您有Count，0汇总返回NULL。无需使用ISNULL功能

Answer 2

这个怎么样

Select m.managerid,
    Case When count(t.employeeid) =0 Then 'No Manager' Else count(m.managerid) end  
From 
    employee t Left Join employenrol m On t.employeeid=m.employeeid 
Group By t.employeeid

Answer 3

我认为这是你想做的事情。

SELECT  t.employeeid,
        CASE WHEN COUNT(m.managerid) = 0 THEN 'No Manager'
             ELSE CAST(COUNT(m.managerid) AS VARCHAR(10))
        END
FROM    employee t
        LEFT JOIN employenrol m ON t.employeeid = m.employeeid
GROUP BY t.employeeid

不确定为什么你会选择m.managerid并计算t.employeeid哪个会产生错误，因为你只是按t.employeeid进行分组

这甚至可能对你有好处

SELECT  t.employeeid,
        CASE WHEN m.managercount = '0' THEN 'No Manager'
             ELSE m.managercount
        END
FROM    @employee t
        OUTER APPLY (SELECT CAST(COUNT(managerid) AS VARCHAR(10)) managercount
                     FROM   @employenrol m
                     WHERE  t.employeeid = m.employeeid
                    ) m

在case语句SQL中计数

3 个答案: