Question

我在创建触发器时遇到困难，该触发器更新了已注册的学生数量。以下是我的表格设置方式。第一段代码由我的导师提供。每当学生注册或被删除时，register_count表都需要使用适当的学生注册数量进行更新。

Create table Registered
(
    ssn numeric,
    code char(10),
    year int,
    semester char(10),
foreign key (ssn) references Student(ssn),
foreign key (code) references Course(code),
    primary key (ssn,code,year,semester)
);

create table Register_Count
(
    code char(10),
    year int,
    semester char(10),
    count int default 0,
    primary key (code, year, semester)
);

这是我到目前为止触发的尝试。我不断得到'多部分标识符无法绑定错误。'

 CREATE TRIGGER updateCount ON registered
    AFTER UPDATE, DELETE, INSERT
    AS
    UPDATE register_count SET 
        code = (select code from inserted), 
        year = (select year from inserted),
        semester = (select semester from inserted), 
        count = (select count(*) from registered) 
    WHERE Register_Count.code = inserted.code
GO

Answer 1

您可以拥有区分大小写的排序规则，您需要更改该行：

WHERE Register_Count.code = inserted.code

为：

WHERE register_count.code = inserted.code

在这种情况下，虽然您正在更新register_count，但您在WHERE子句中有一个对'inserted'的引用，您在UPDATE语句中没有引用它。

我想你想要这样的东西：

UPDATE register_count 
from register_count inner join inserted
on Register_Count.code = inserted.code
SET 
code = inserted.code, 
year = inserted.year,
semester = inserted.semester, 
count = (select count(*) from registered)

跨表的SQL触发器

1 个答案: