比较运算符在 Case 语句中的使用

Question

当我尝试在 SQL Server 中使用以下查询时，我遇到了一些语法问题。我想根据条件显示WHERE 子句。

这是我的代码：

DECLARE @isActual = 0

SELECT
    SolverRunId, PointId, TimeStampUtc, Value,
    UnitOfMeasure, Reliability
FROM
    (SELECT 
         bt.SolverRunId, bt.PointId, bt.TimeStampUtc,
         bt.Value, bt.UnitOfMeasure, bt.Reliability
     FROM 
         cte bt
     WHERE 
         bt.TimeStampUtc = bt.TargetTimeUtc

     UNION ALL

     SELECT 
         a.SolverRunId, a.PointId, a.TimeStampUtc, a.Value,
         a.UnitOfMeasure, a.Reliability
     FROM 
         cte a
     WHERE 
         -- I tried using this case but it is syntactically incorrect
         CASE 
             WHEN @isActual = 0 THEN a.TimeStamUtc > @endDateUtc 
             ELSE a.TimestampUtc <= @endDateUtc 
         END
         -- instead of this. I wanted to have conditional where based on @isActual value from 0 to 1
         a.TimeStampUtc > @endDateUtc
         AND a.SolverRunId = @maxRun) x
ORDER BY 
    SolverRunId, PointId, TimeStampUtc;

我希望将基于 @isActual 评估的 where 条件设置为 true 或 false

Answer 1

如 cmets 中所述，不要在 WHERE 中使用 CASE，只需使用带有 AND 和 OR 子句的适当布尔逻辑即可。在您的问题中，您的变量 @isActual 也缺少数据类型，所以我 假设它是 bit：

DECLARE @isActual bit = 0;
SELECT SolverRunId,
       PointId,
       TimeStampUtc,
       Value,
       UnitOfMeasure,
       Reliability
FROM (SELECT bt.SolverRunId,
             bt.PointId,
             bt.TimeStampUtc,
             bt.Value,
             bt.UnitOfMeasure,
             bt.Reliability
      FROM cte bt
      WHERE bt.TimeStampUtc = bt.TargetTimeUtc
      UNION ALL
      SELECT a.SolverRunId,
             a.PointId,
             a.TimeStampUtc,
             a.Value,
             a.UnitOfMeasure,
             a.Reliability
      FROM cte a
      WHERE a.TimeStampUtc > @endDateUtc
        AND a.SolverRunId = @maxRun
        AND ((@isActual = 0 AND a.TimeStamUtc > @endDateUtc)
          OR (@isActual = 1 AND a.TimestampUtc <= @endDateUtc))) x
ORDER BY SolverRunId,
         PointId,
         TimeStampUtc;

您可能还想尝试将RECOMPILE 添加到上面的OPTION 子句中，因为当@isActual 具有1 或0 的值时的查询计划要求可能完全不同。