将 mySQL 触发器转换为 SQL

Question

寻求帮助将此 mySQL 触发器转换为 TSQL。

CREATE TRIGGER IF not exists TF_WATCHLIST_PERSISTENCE_ADD_POSITION 
AFTER INSERT ON TF_WATCHLIST_PERSISTENCE
FOR EACH ROW
WHEN NEW.WATCHLIST_POSITION IS NULL
BEGIN 
    UPDATE TF_WATCHLIST_PERSISTENCE SET
    WATCHLIST_POSITION = (SELECT COUNT(*) - 1 FROM TF_WATCHLIST_PERSISTENCE WHERE WATCHLIST_USER = NEW.WATCHLIST_USER)
    WHERE rowid = NEW.rowid;
END;

Answer 1

感谢大家的帮助

我最终得到了这个。

CREATE TRIGGER TF_WATCHLIST_PERSISTENCE_ADD_POSITION 
ON TF_WATCHLIST_PERSISTENCE
AFTER INSERT, UPDATE
AS
DECLARE @MyCursor CURSOR;
DECLARE @MyField_USER varchar(250);
DECLARE @MyField_ID varchar(250);
DECLARE @MyField_NewPos int

BEGIN 
SET @MyCursor = CURSOR FOR 
SELECT      WATCHLIST_USER
        ,   WATCHLIST_ID
FROM    inserted
WHERE inserted.WATCHLIST_POSITION is null

OPEN @MyCursor 
FETCH NEXT FROM @MyCursor
INTO @MyField_USER,  @MyField_ID

WHILE @@FETCH_STATUS = 0

BEGIN 
    set @MyField_NewPos = (SELECT MAX(WATCHLIST_POSITION) + 1 FROM TF_WATCHLIST_PERSISTENCE WHERE WATCHLIST_USER = @MyField_USER)
    print @MyField_NewPos

    update TF_WATCHLIST_PERSISTENCE 
        SET WATCHLIST_POSITION = ISNULL(@MyField_NewPos,0)
        WHERE       WATCHLIST_USER = @MyField_USER 
            AND     WATCHLIST_ID = @MyField_ID
            AND     WATCHLIST_POSITION IS NULL 

        Print @MyField_USER 
        Print @MyField_ID
        FETCH NEXT FROM @MyCursor
        INTO @MyField_USER,  @MyField_ID
END;


END;
CLOSE @MyCursor

Answer 2

我怀疑您正在寻找排名功能，甚至是每个用户的简单COUNT(*)？ MySQL 在analytic、ranking 或窗口函数方面相当差，因此使用古怪的更新或触发器等技巧来模拟它们。

在 SQL Server 中，您可以返回与每行中单个用户匹配的记录数，并将COUNT() 应用于匹配单个用户的记录：

SELECT *, COUNT(*) OVER (PARTITION BY WATCHLIST_USER)
FROM TF_WATCHLIST_PERSISTENCE 

不需要触发器。您可以使用任何带有 OVER() 子句的聚合。

如果您希望按照某种顺序排名，您可以使用ROW_NUMBER() 或`RANK() 等排名函数之一。如果你想计算每个用户的行位置，例如在创建日期，你可以写：

SELECT *, ROW_NUMBER(*) OVER (PARTITION BY WATCHLIST_USER ORDER BY CreationDate)
FROM TF_WATCHLIST_PERSISTENCE 

如果您有一个递增的 ID，您可以使用它为每个用户生成一个 row position

SELECT *, ROW_NUMBER(*) OVER (PARTITION BY WATCHLIST_USER ORDER BY ID)
FROM TF_WATCHLIST_PERSISTENCE 

大多数时候，您不需要存储行位置。向查询添加排名函数很简单。

如果您确实需要在表格中存储这样的行位置，您可以使用简单的多行触发器

CREATE TRIGGER TF_WATCHLIST_PERSISTENCE_ADD_POSITION 
ON TF_WATCHLIST_PERSISTENCE
AFTER INSERT, UPDATE
AS
    update TF_WATCHLIST_PERSISTENCE 
    set WATCHLIST_POSITION =ROW_NUMBER() OVER (PARTITION BY WATCHLIST_USER ORDER BY ID)
    FROM inserted 
    INNER JOIN TF_WATCHLIST_PERSISTENCE on inserted.ID=TF_WATCHLIST_PERSISTENCE.ID

或者

update TF_WATCHLIST_PERSISTENCE 
set WATCHLIST_POSITION =ROW_NUMBER() OVER (PARTITION BY WATCHLIST_USER ORDER BY ID)
FROM inserted 
INNER JOIN TF_WATCHLIST_PERSISTENCE 
    ON inserted.WATCHLIST_USER =TF_WATCHLIST_PERSISTENCE.WATCHLIST_USER 

如果您想为现有用户插入新条目并重新计算所有位置

Answer 3

试试这个：

CREATE TRIGGER TF_WATCHLIST_PERSISTENCE_ADD_POSITION ON TF_WATCHLIST_PERSISTENCE  AFTER INSERT 
AS
BEGIN 
    WITH DataSource AS
    (
        SELECT DS.WATCHLIST_USER
              ,COUNT(*) - 1 AS WATCHLIST_POSITION
        FROM TF_WATCHLIST_PERSISTENCE DS
        INNER JOIN inserted I
            ON DS.WATCHLIST_USER = I.WATCHLIST_USER
        WHERE inserted.WATCHLIST_POSITION is null
        GROUP BY DS.WATCHLIST_USER
    )
    UPDATE TF_WATCHLIST_PERSISTENCE
    SET WATCHLIST_POSITION = DS.[WATCHLIST_POSITION]
    FROM TF_WATCHLIST_PERSISTENCE DS
    INNER JOIN DataSource I
        ON DS.WATCHLIST_USER = I.WATCHLIST_USER;
END