具有多个条件的 case 语句答案

【问题标题】：Case statement with more than one condition具有多个条件的 case 语句
【发布时间】：2015-11-13 18:27:15
【问题描述】：

我需要根据访问天数从表中获取记录。如何通过更正下面的查询来实现这一点？它有语法错误。我知道语法不正确，但它会让您了解我想要实现的目标。

DECLARE @PatientByDate INT
 SET @PatientByDate  = 30
    SELECT * FROM Visits
     WHERE
    CASE  
           WHEN(@PatientByDate = 90) then DaysVisited > 90
           WHEN(@PatientByDate = 60) then DaysVisited >= 60 AND DaysVisited < 90
           WHEN(@PatientByDate = 30) then DaysVisited >= 30 AND DaysVisited < 60
           WHEN(@PatientByDate = 25) then DaysVisited < 30
           WHEN(@PatientByDate = 0) then -500 AND <= 5000000
      END

【问题讨论】：

检查stackoverflow.com/questions/24254164/sql-case-when-and
CASE 不是语句 - 它是表达式（可以返回各种可能值之一）。您不能从 CASE 返回“代码块”或条件 - 只能返回单个原子值。

标签： sql sql-server

【解决方案1】：

直接将谓词与or结合起来：

SELECT * FROM Visits
WHERE
    (@PatientByDate = 90 and DaysVisited > 90) or
    (@PatientByDate = 60 and DaysVisited >= 60 and DaysVisited < 90) or
    (@PatientByDate = 30 and DaysVisited >= 30 and DaysVisited < 60) or
    (@PatientByDate = 25 and DaysVisited < 30) or
    (@PatientByDate in(0, -500))

【讨论】：

【解决方案2】：

您必须将它们全部移至 When 子句并将其与返回值匹配 (=1)：

DECLARE @PatientByDate INT
SET @PatientByDate  = 30
SELECT * FROM Visits
WHERE 1 = CASE  
    WHEN(@PatientByDate = 90) AND DaysVisited > 90 then 1 
    WHEN(@PatientByDate = 60) AND DaysVisited >= 60 AND DaysVisited < 90 then 1 
    WHEN(@PatientByDate = 30) AND DaysVisited >= 30 AND DaysVisited < 60 then 1 
    WHEN(@PatientByDate = 25) AND DaysVisited < 30 then 1 
    WHEN(@PatientByDate = 0) AND -500 AND <= 5000000 then 1 
END

或者干脆做：

DECLARE @PatientByDate INT
SET @PatientByDate  = 30
SELECT * FROM Visits
WHERE 
    ((@PatientByDate = 90) AND DaysVisited > 90) OR 
    ((@PatientByDate = 60) AND DaysVisited >= 60 AND DaysVisited < 90) OR 
    ((@PatientByDate = 30) AND DaysVisited >= 30 AND DaysVisited < 60) OR
    ((@PatientByDate = 25) AND DaysVisited < 30) OR
    ((@PatientByDate = 0) AND -500 AND <= 5000000)

【讨论】：