Question

I would to create a trigger for Sybase, but it shows an error.

What I want to do is, when a delete operation is done on the [student] table, to check whether there is any record related to student on [account], and if so, raise an exception.

There seems to be a lack of support by Sybase. Their official seem not people to visit.

*CREATE TRIGGER AccountChecker BEFORE DELETE ON student REFERENCING OLD AS old_student FOR EACH ROW  BEGIN DECLARE @acc CHAR(4); DECLARE @acc_not_null EXCEPTION FOR SQLSTATE '99999';  SELECT @acc=account.account_number FROM account WHERE account.student_id = old_student.student_id;     IF @acc IS NOT NULL    BEGIN     SIGNAL acc_not_null    END  END* 

Answer 1

Sybase supports foreign keys and primary keys, both via procedures such as sp_primarykey and sp_foreignkey and via declarative SQL constraints. What you are seeking to do is exactly what a foreign key from [account] referencing [student] should do.

The Sybase SQL User Guide (Adaptive Server 15, if it matters) illustrates a ‘delete restricted’ trigger (with somewhat different indentation):

create trigger deltitle     on titles     for delete     as        if (select count(*)                from deleted, salesdetail                where salesdetail.title_id =                deleted.title_id) > 0        begin            rollback transaction            print 'You cannot delete a title with sales.'        end 

I’m not convinced that rollback is a good idea; an exception is probably better.

The notation you are trying to use hews more closely to the SQL standard than the documented Sybase-supported notation.