数据库触发器或应用程序代码？ 在这种情况下，我应该使用哪一个？

Question

Using c# and mssql 2008 R2, I have a service that inserts a user into the system, users have a unique number assigned to them which is something like a1, b1 or c1 which will get increased on user insertion but before insertion I have to check whether there is any previous unique number available or not( unique numbers can be deleted on user deletion). For example if there are 5 users in the database, a1,...,a5 are reserved and if you delete lets say 3rd user then a3 will be available for next user insertion. This can be done easily but since I have to read the available unique numbers on every insertion , I'm puzzled whether it's better to use insert trigger or use application code before insertion ?

Thanks in advance

Answer 1

I'm not sure about triggers and how you want to do it this way but you can definitely achieve that in the code/stored proc. This will be a 2 step process that will have to be in one transaction:

• select the minimum available ID
• insert the new record

One important thing is that you will want to lock the table during the select query to prevent other processes obtaining the same ID. You can do that using exclusive lock hint. The code might look like:

select min(T.ID) + 1 from TableName T with(xlock)
     where not exists (select * from TableName T1 where T1.ID = T.ID + 1)