我无法在 Microsoft SQL Server 2014 中创建正确的触发器

Posted 2023-05-08

【中文标题】我无法在 Microsoft SQL Server 2014 中创建正确的触发器

【英文标题】：I am having trouble creating a proper trigger in Microsoft SQL Server 2014

【发布时间】：2017-11-16 03:38:00

【问题描述】：

我正在尝试在tplayoffStatus 上创建一个触发器，这样一来，团队就不能被插入到表中，并且损失超过一次。将值插入表 tplayoffStatus 时，我不断收到的错误是

子查询返回超过 1 个值。当子查询跟随 =、!=、、>= 或子查询用作表达式时，这是不允许的。

谁能帮我解决这个问题？我的 SELECT 语句在 loss 列中返回多个值是否错误？

SQL Server 2014 表架构：

CREATE TABLE tcollegeFootballTeams
(
    TeamAbbreviation varchar(5) NOT NULL PRIMARY KEY,
    TeamName varchar(50) NOT NULL,
    City varchar(50) NOT NULL,
    State varchar(2) NOT NULL,
    Wins int NOT NULL,
    Losses int NOT NULL
)  

CREATE TABLE tplayoffStatus
(
    TeamName varchar(50) NOT NULL PRIMARY KEY,
    TeamAbbreviation varchar(5) NOT NULL FOREIGN KEY REFERENCES tcollegeFootballTeams(TeamAbbreviation)
); 

CREATE TRIGGER [dbo].[trgNoPlayoffForYou] 
ON [dbo].[tplayoffStatus]
AFTER INSERT
AS
    DECLARE @Losses INT
    DECLARE @ErrorMessage VARCHAR(30)

    SELECT @Losses = (SELECT Losses 
                      FROM dbo.tcollegeFootballTeams 
                      WHERE (Losses > 1))

    IF (@Losses = 'True') 
    BEGIN
        SET @ErrorMessage = 'You may not enter the playoffs with more than 1 loss'
        PRINT @ErrorMessage
        ROLLBACK TRANSACTION
    END

查询 1：

INSERT INTO tcollegeFootballTeams (TeamAbbreviation, TeamName, City, State, Wins, Losses)
VALUES ('OSU', 'THE Ohio State University', 'Columbus', 'OH', 10, 2)

[结果][2]

查询 2：

INSERT INTO tcollegeFootballTeams (TeamAbbreviation, TeamName, City, State, Wins, Losses  )
VALUES ('BAMA', 'Alabama', 'Tuscaloosa', 'AL', 12, 0)

[结果][3]

查询 3：

INSERT INTO tcollegeFootballTeams (TeamAbbreviation, TeamName, City, State, Wins, Losses  )
VALUES ('UGA', 'Georgia', 'Athens', 'GA', 11, 1)

[结果][4]

查询 4：

INSERT INTO tcollegeFootballTeams (TeamAbbreviation, TeamName, City, State, Wins, Losses)
VALUES ('CLEM', 'Clemson', 'Clemson', 'SC', 11, 1)

[结果][5]

查询 5：

INSERT INTO tcollegeFootballTeams (TeamAbbreviation, TeamName, City, State, Wins, Losses)
VALUES ('WIS', 'Wisconsin', 'Madison', 'WI', 11, 1)

[结果][6]

查询 6：

INSERT INTO tcollegeFootballTeams (TeamAbbreviation, TeamName, City, State, Wins, Losses)
VALUES ('ND', 'Notre Dame', 'South Bend', 'IN', 10, 2)

[结果][7]

查询 7：

INSERT INTO tcollegeFootballTeams (TeamAbbreviation, TeamName, City, State, Wins, Losses)
VALUES ('OKLA', 'Oklahoma', 'Norman', 'OK', 10, 2)

[结果][8]

查询 8：

INSERT INTO tcollegeFootballTeams (TeamAbbreviation, TeamName, City, State, Wins, Losses)
VALUES ('MIAF', 'Miami of Florida', 'Coral Gables', 'FL', 10, 2)

【参考方案1】：

你的触发器是错误的。您需要在inserted 表中查询插入的记录，并在tcollegeFootballTeams 表中加入Losses

CREATE TRIGGER [dbo].[trgNoPlayoffForYou] ON [dbo].[tplayoffStatus]
AFTER INSERT
AS

    IF EXISTS
       (
           SELECT *
           FROM   inserted i
                  INNER JOIN dbo.tcollegeFootballTeams t 
                  ON i.TeamAbbreviation = t.TeamAbbreviation
           WHERE  t.Losses > 1
       )
    BEGIN 
           SET  @ErrorMessage = 'You may not enter the playoffs with more than 1 loss'
           Print @ErrorMessage
           Rollback Transaction
    END

【讨论】：

这行得通。谢谢你。我什至没有想过要使用这样的选择语句，但这完全有道理。我显然需要处理我的 SQL 的这方面。