基于另一个表的唯一ID自动增加表的字母数字ID

Question

我想根据学生的部门为学生生成一个唯一的ID。 我希望当部门ID为CS时，学生ID为CS0448，部门ID为IT时为IT0448，依此类推。这些ID必须增加1。

我认为我会有另一个身份并自动增加1，每个学生添加并与部门ID连接，但这不会帮助我。这将导致IT学生在CS0448旁边添加为IT0449。请帮我解决一下这个。看到这个......一定是这样的......

...
cs0439
it0441
cs0440
it0442
cs0441
cs0442

请告诉我更好的字母数字标识选项

Answer 1

您可以使用trigger BEFORE insert，根据您的逻辑更改ID的值。

基本上你会做正常的选择以获得你已经拥有的下一个ID和类型（IT或CS）（我认为）。

Answer 2

您可以尝试INSTEAD OF INSERT触发器，如下所示：

create table students(id varchar(10) primary key not null, Department varchar(2), Name varchar(80))
go

create trigger students_insert_PK
    on students
    INSTEAD OF INSERT
as
    declare @id int;
    declare @dept varchar(2); select @dept=Department from INSERTED;
    select @id=cast(max(right(id,4)) as int) from students where Department=@dept;
    set @id=isnull(@id,0)+1;

    insert into students
    select Department+right('0000'+cast(@id as varchar(4)),4)
    , Department
    , name
    from INSERTED;
go

insert into students (Department,Name) values ('CS','John');
insert into students (Department,Name) values ('CS','Pat');
insert into students (Department,Name) values ('CS','Sheryl');
insert into students (Department,Name) values ('IT','Phil');
insert into students (Department,Name) values ('EE','Frank');
insert into students (Department,Name) values ('EE','Amy');
insert into students (Department,Name) values ('EE','Stu');
go

select * from students;
go

结果：