sql - 在存储过程中重用 SELECT 查询的结果

Question

这可能是一个非常简单的问题，但我搜索答案的尝试被谷歌阻止，谷歌找到的答案展示了如何通过创建存储过程来重用查询。我想在存储过程中重用查询结果。

这是一个精简示例，其中我删除了 NOCOUNT、XACT_ABORT、TRANSACTION、TRY ，以及大部分逻辑。

CREATE PROCEDURE Do_Something
    @userId UNIQUEIDENTIFIER
AS
BEGIN

    DELETE FROM LikedItems
    WHERE likedItemId IN
    (
        SELECT Items.id FROM Items
        WHERE Items.userId = @userId
    )

    DELETE FROM FollowedItems
    WHERE followedItemId IN
    (
        SELECT Items.id FROM Items
        WHERE Items.userId = @userId
    )

END

重用重复嵌套SELECT结果而不是执行两次的语法是什么？

Answer 1

您可以将 SELECT 的结果 INSERT 到临时表或表变量中，但这并不自动意味着整体性能会更好。您需要测量它。

临时表

CREATE PROCEDURE Do_Something
    @userId UNIQUEIDENTIFIER
AS
BEGIN

    CREATE TABLE #Temp(id int);

    INSERT INTO #Temp(id)
    SELECT Items.id 
    FROM Items
    WHERE Items.userId = @userId;

    DELETE FROM LikedItems
    WHERE likedItemId IN
    (
        SELECT id FROM #Temp
    )

    DELETE FROM FollowedItems
    WHERE followedItemId IN
    (
        SELECT id FROM #Temp
    )

    DROP TABLE #Temp;

END

表变量

CREATE PROCEDURE Do_Something
    @userId UNIQUEIDENTIFIER
AS
BEGIN

    DECLARE @Temp TABLE(id int);

    INSERT INTO @Temp(id)
    SELECT Items.id 
    FROM Items
    WHERE Items.userId = @userId;

    DELETE FROM LikedItems
    WHERE likedItemId IN
    (
        SELECT id FROM @Temp
    )

    DELETE FROM FollowedItems
    WHERE followedItemId IN
    (
        SELECT id FROM @Temp
    )

END