Question

我有以下查询：

SELECT  CASE
   WHEN @from < item.UpdatedOnCurr AND item.UpdatedOnCurr <= @till AND @till < item.UpdatedOnNext
       THEN item.Id
   ELSE '00000000-0000-0000-0000-000000000000'
        END AS Id,
        CASE
            WHEN @from < item.UpdatedOnCurr AND item.UpdatedOnCurr <= @till AND @till < item.UpdatedOnNext
            THEN item.PreviousId
            ELSE item.Id
        END AS PreviousId,
        item.UUID,
        CASE
            WHEN @from < item.UpdatedOnCurr AND item.UpdatedOnCurr <= @till AND @till < item.UpdatedOnNext
            THEN item.Json
            ELSE NULL
        END AS Json,
        item.TableName,
        item.PermissionId,
        item.UpdatedOnCurr

FROM Computed item
WHERE item.Json IS NOT NULL AND (
        (@from < item.UpdatedOnCurr AND item.UpdatedOnCurr <= @till AND @till < item.UpdatedOnNext)
    OR (item.UpdatedOnCurr <= @from AND @from < item.UpdatedOnNext AND item.UpdatedOnNext <= @till)
);

我想简化它，即所有那些多个CASE表达式都会削弱我的眼球，所以我想重新使用@from < item.UpdatedOnCurr AND item.UpdatedOnCurr <= @till AND @till < item.UpdatedOnNext检查以便它赢得了＃t每个选定的行执行多次......

那么你是如何实现这一目标的？

Answer 1

使用 APPLY ，您可以清除其中一些重复逻辑。 CASE仍在那里..但我发现它更具可读性。

SELECT  CASE m.m
            WHEN 1
            THEN item.Id
            ELSE '00000000-0000-0000-0000-000000000000'
        END AS Id,
        CASE m.m
            WHEN 1
            THEN item.PreviousId
            ELSE item.Id
        END AS PreviousId,
        item.UUID,
        CASE m.m
            WHEN 1
            THEN item.Json
            ELSE NULL
        END AS Json,
        item.TableName,
        item.PermissionId,
        item.UpdatedOnCurr

FROM Computed item
CROSS APPLY (
    select
        CASE
            WHEN @from < item.UpdatedOnCurr AND item.UpdatedOnCurr <= @till AND @till < item.UpdatedOnNext
            THEN 1
            ELSE 0 
        END m
) m
WHERE item.Json IS NOT NULL AND (
        (@from < item.UpdatedOnCurr AND item.UpdatedOnCurr <= @till AND @till < item.UpdatedOnNext)
    OR (item.UpdatedOnCurr <= @from AND @from < item.UpdatedOnNext AND item.UpdatedOnNext <= @till)
);

在＆＃34;中选择＆＃34;简化多个重复的案例表达。和＆＃34;其中＆＃34;

1 个答案: