Question

I need a trigger that updates a table row field if one or more fields of that row is updated.

Suppose you have an Employees table that may look as follows:

EmployeeId    Name       Address                ModificationDate
1             Spears     27 Sober Road 
2             Jagger     65 Straight Street 

If there is a real change in the value of any field except the EmployeeId and ModificationDate fields, the trigger should generate a time value and update the ModificationDate.

Example 1 of a real change:

update dbo.Employees
set Name = 'Beggar'
where EmployeeId = 2

Example 2 of no real change:

update dbo.Employees
set Name = 'Jagger'
where EmployeeId = 2

If an update in Example 2 executes, the trigger should not update the ModificationDate field.

Answer 1

In a trigger, you have access to the ‘inserted’ and ‘deleted’ system tables.
Those tables contains the records in the table that have been updated by the statement that caused the trigger to execute.

For an ‘UPDATE’ trigger, the ‘inserted’ table contains the records like they are in the new state, the ‘deleted’ table contains the records with the old values.

You’ll have to make use of those 2 tables to find out which records have really changed, and update the ModificationDate for those records.

I think the statement inside the trigger will look something like this. (I haven’t tested it)

UPDATE myTable
SET ModificationDate = getdate()
FROM inserted, deleted
WHERE inserted.EmployeeId = deleted.EmployeeId
AND (inserted.Name <> deleted.Name OR inserted.Address <> deleted.Address)

---

Edit:
I’ve played around a bit:

create trigger upd_employee on [employee] after update
as
begin

    update employee
    set modifdate = getdate()   
    where employee.empid in 
    ( select i.empid
      from inserted i
      inner join deleted d on i.empid = d.empid 
      where (i.name <> d.name or i.address <> d.address )
    )
end

insert into employee 
values
(1, 'Frederik' , '', null)

insert into employee
values
(2, 'User', '', null)

update employee
set [address] = 'some address'

select * from employee

update employee set [name] = 'test' where empid = 2

select * from employee

update employee set [name] = 'test' where empid = 2

select * from employee