Where 子句 TSQL 中的 case 表达式

Posted 2023-03-29

【中文标题】Where 子句 TSQL 中的 case 表达式

【英文标题】：Case expression in Where Clause TSQL

【发布时间】：2020-01-03 19:34:02

【问题描述】：

我正在尝试在 where 子句中编写一个 case 表达式，但我无法让语法正确地用于我想做的事情。在 where 子句中，我想让 case 语句检查“IndividualRateOption”列，并根据该列添加到 where 子句中。

--- Get generic rates
            select  case when RateType = 'PRE' then 1
                         when RateType = 'RID' then 2
                         when RateType = 'QUL' then 3 end,
                    BillingEntityId,
                    @GroupID,
                    RateID,
                    TierItemId,
                    RateUnitType,
                    RateUnitValue,
                    RateType,
                    RateTypeEntityID,
                    EffectiveDate,
                    ExpirationDate,
                    Usage,
                    AgeFrom,
                    AgeTo,
                    Gender,
                    PayBrokerCommissions
              from #BillingEntityRates
             where case IndividualRateSelectionOption when 'ANV' then @AnniversaryDate between EffectiveDate and ExpirationDate
                    OR isnull(@AnniversaryDate,@MemberEligibilityDate) between EffectiveDate and ExpirationDate
                    and EntityId is null

如果 IndividualRateSelectionOption 为 'ANV' 我想根据“@anniversaryDate 在 Effective 和 ExpirationDate 之间且 EntityId 为空”进行过滤

如果 IndividualRateSelectionOption 不是“ANV”，我想根据 EffectiveDate 和 ExpirationDate 之间的“isnull(@AnniversaryDate,@MemberEligibilityDate) 进行过滤 并且 EntityId 为空”

以上是我迄今为止尝试过的，但它抱怨语法。提前致谢。

【问题讨论】：

我不认为你真的需要一个案例陈述。 Just WHERE (x = 'ANV' AND date between x and y and id IS NULL) OR (x != 'ANV' AND date between x and y and id IS NULL)

虽然它可能对当前查询没有帮助，但this 答案显示了如何在on 子句中使用case 表达式。 where 子句的工作方式相同。

【参考方案1】：

当更简单的布尔逻辑起作用时，不要使用case：

where (IndividualRateSelectionOption = 'ANV' and 
       @anniversaryDate between Effective and ExpirationDate and
       EntityId is null
      ) or
      (IndividualRateSelectionOption <> 'ANV' and 
       coalesce(@AnniversaryDate, @MemberEligibilityDate) between EffectiveDate and ExpirationDate and
       EntityId is null
      )

你可以过滤掉EntityId is null逻辑：

where EntityId is null and
      ( (IndividualRateSelectionOption = 'ANV' and 
         @anniversaryDate between Effective and ExpirationDate          
        ) or
        (IndividualRateSelectionOption <> 'ANV' and 
         coalesce(@AnniversaryDate, @MemberEligibilityDate) between EffectiveDate and ExpirationDate and
        )
      )