SQL Server 2008 - Help writing simple INSERT Trigger

Question

This is with Microsoft SQL Server 2008.

I've got 2 tables, Employee and EmployeeResult and I'm trying to write a simple INSERT trigger on EmployeeResult that does this - each time an INSERT is done into EmployeeResult such as:

(Jack, 200, Sales) (Jane, 300, Marketing) (John, 400, Engineering)

It should look up for the Name, Department entry pairs, such as

(Jack, Sales), (Jane, Marketing), (John, Engineering)

within the Employee table, and if such an employee does not exist, should insert that into the Employee table.

What I have is this with unknowns on how to fix the "???"s:

CREATE TRIGGER trig_Update_Employee
ON [EmployeeResult]
FOR INSERT
AS
IF EXISTS (SELECT COUNT(*) FROM Employee WHERE ???)
  BEGIN
   INSERT INTO [Employee] (Name, Department) VALUES (???, ???)
  END

Please help, thanks in advance

Schema:

Employee
--------
Name, varchar(50)
Department, varchar (50)

EmployeeResult
--------------
Name, varchar(50)
Salary, int
Department, varchar (50)

Answer 1

You want to take advantage of the inserted logical table that is available in the context of a trigger. It matches the schema for the table that is being inserted to and includes the row(s) that will be inserted (in an update trigger you have access to the inserted and deleted logical tables which represent the the new and original data respectively.)

So to insert Employee / Department pairs that do not currently exist you might try something like the following.

CREATE TRIGGER trig_Update_Employee
ON [EmployeeResult]
FOR INSERT
AS
Begin
    Insert into Employee (Name, Department) 
    Select Distinct i.Name, i.Department 
    from Inserted i
    Left Join Employee e
    on i.Name = e.Name and i.Department = e.Department
    where e.Name is null
End

Answer 2

cmsjr had the right solution. I just wanted to point out a couple of things for your future trigger development. If you are using the values statement in an insert in a trigger, there is a stong possibility that you are doing the wrong thing. Triggers fire once for each batch of records inserted, deleted, or updated. So if ten records were inserted in one batch, then the trigger fires once. If you are refering to the data in the inserted or deleted and using variables and the values clause then you are only going to get the data for one of those records. This causes data integrity problems. You can fix this by using a set-based insert as cmsjr shows above or by using a cursor. Don't ever choose the cursor path. A cursor in a trigger is a problem waiting to happen as they are slow and may well lock up your table for hours. I removed a cursor from a trigger once and improved an import process from 40 minutes to 45 seconds.

You may think nobody is ever going to add multiple records, but it happens more frequently than most non-database people realize. Don't write a trigger that will not work under all the possible insert, update, delete conditions. Nobody is going to use the one record at a time method when they have to import 1,000,000 sales target records from a new customer or update all the prices by 10% or delete all the records from a vendor whose products you don't sell anymore.