我是否被迫使用 CTE 或存储过程而不是视图？

Question

我想减少我的代码的大小并有一个查询 运行尽可能快。

我在同一个 SELECT 中多次复制粘贴了一个 CASE 表达式。这是多余的，可能运行切换多次而不是一次，使其比应有的速度慢（或者不是吗？SQL 图是否检测到冗余代码并重用结果？）

-- My view.
SELECT
    /* 20 lines case expression */ + 1 AS a,
    /* 20 lines case expression */ + 2 AS b,
    /* 20 lines case expression */ + 3 AS c,
    /* 20 lines case expression */ + 4 AS d,
FROM some_table

为了避免重复自己，我想做以下事情：

-- The following code is not valid. It is meant to represent my goal.
SELECT @temp := /* 20 lines case expression */ AS complex
FROM some_table;

SELECT
    @temp + 1 AS a,
    @temp + 2 AS b,
    @temp + 3 AS c,
    @temp + 4 AS d,
FROM some_table

但是您可能知道，用户定义的变量与视图无关。此外，CTE 通常被描述为缓慢（我不知道在何种程度上和在何种情况下）。

我想单独使用一个视图，可以吗？（速度更重要）如果不行，那也没关系，我就做下面的一个。

只保留copy/pasted代码
对 case 表达式使用存储过程（增加了使数据库混乱的许多过程）
简单地使用 CTE（因为在这种情况下它可能很快？）

感谢您的帮助并分享您解决此问题的方法。

更新：

根据您的要求，这是我正在处理的一个更实际的例子。它基于遗留代码，请不要相信我。

-- It's a simplified example with small alterations.
SELECT
    -- Nothing special ...
    [col_x] AS X,
    [col_y] AS Y,
    [col_z] AS Z,
    -- Then there is this column...
    CASE
        WHEN
            [col_a] + ' ' +
            CASE
                WHEN [col_b] = 'some_code' THEN 'something'
                ELSE 'something_else'
            END + ' ' +
            CASE
                WHEN [col_c] IN ('a', 'b', 'c') THEN 'something'
                ELSE 'something_else'
            END = 'First thing to compare with'
        THEN [return_First],
        WHEN
            [col_a] + ' ' +
            CASE
                WHEN [col_b] = 'some_code' THEN 'something'
                ELSE 'something_else'
            END + ' ' +
            CASE
                WHEN [col_c] IN ('a', 'b', 'c') THEN 'something'
                ELSE 'something_else'
            END = 'Second thing to compare with'
        THEN [return_Second],
        WHEN
            [col_a] + ' ' +
            CASE
                WHEN [col_b] = 'some_code' THEN 'something'
                ELSE 'something_else'
            END + ' ' +
            CASE
                WHEN [col_c] IN ('a', 'b', 'c') THEN 'something'
                ELSE 'something_else'
            END = 'Second thing to compare with'
        THEN [return_Third]
    END AS [Monster Case Expression That Makes Me Cry]
FROM some_table

Answer 1

最好的方法是将表达式放在 APPLY 中，这意味着您可以在查询中的任何地方重复使用它：

SELECT
    v1.Temp + 1 AS a,
    v1.Temp + 2 AS b,
    v1.Temp + 3 AS c,
    v1.Temp + 4 AS d,
FROM some_table
CROSS APPLY (VALUES (
    CASE WHEN /* 20 lines case expression */
    END
) ) AS v1(Temp)

Answer 2

就这么简单：

SELECT 
    CaseColumn + 1 AS a,
    CaseColumn + 2 AS b,
    CaseColumn + 3 AS c,
    CaseColumn + 4 AS d
FROM (
    SELECT
        /* 20 lines case expression */ AS CaseColumn
    FROM some_table
)

我是否被迫使用 CTE 或存储过程而不是视图？

Am I forced to use a CTE or stored procedure instead of a view?

sql

sql-server

sql-view