Question

I have below sample format table structure:

CUSTOMER table

CUSTID INT,//PRIMARY KEY
CUSTDATA VARCHAR

EMPLOYEE table

EMPID INT,//PRIMARY KEY
EMPDATA VARCHAR

ITEM table

ITEMID INT,//PRIMARY KEY
CUSTID INT,//REFERENCE KEY
ITEMTYPE INT //1 FOR CUSTOMER AND 2 FOR EMPLOYEE
EMPID INT

MERGEDATA table

MERGEID INT,
CUSTDATA VARCHAR,
EMPDATA VARCHAR
ACTION VARCHAR

Above I have four tables (CUSTOMER, EMPLOYEE, ITEM and MERGEDATA), now I want to create SQL Server trigger on the ITEM table for INSERT/UPDATE/DELETE events, so whenever activity is done on the ITEM table it populates my MERGEDATA table with the action done on ITEM table.

So if any new rows get inserted into the ITEM table a new entry goes into the MERGEDATA table depending on the CUSTOMER or EMPLOYEE entries, like if there is any entry from customer it will add one entry in the ITEM table as well as in CUSTOMER table as below

CUSTOMER table

123, TESTCUSTOMER

ITEM table

1, 123, 1, 0

And same goes for Employee table too, however in the ITEM table row will be like 1, 456, 0, 2.

Now I want to write if condition in Trigger that if there is entry from CUSTOMER table

IF (ITEMTYPE == 1)
//Entry in MERGEDATA will as below

MERGEDATA table

1, 123, 0, ACTION (will depend on type of trigger event trigger if INSERT(ACTION = INS), for update (UPDATE = UPD) etc

So in short I am looking below things in trigger:

• How to write IF condition in trigger
• How to do inner joins from other table in trigger

Please suggest!!

Thanks

Answer 1

My suggestion would be:

create three separate triggers – one for each operation. This makes it easier to determine the Action, and it also gives you the flexibility to turn on/off each operation individually. Furthermore, the trigger code will be smaller, easier to understand, easier to maintain.

Given that design, your trigger will be dead simple:

CREATE TRIGGER trg_Item_Insert 
ON dbo.Item FOR INSERT
AS 
   -- first insert customer-related data - if any
   INSERT INTO dbo.MergeTable(CUSTDATA, EMPDATA, ACTION)
      SELECT CustData, EmptyData, 'INSERT'
      FROM Inserted
      WHERE ITEMTYPE = 1

   -- then insert employee-related data - if any
   INSERT INTO dbo.MergeTable(CUSTDATA, EMPDATA, ACTION)
      SELECT CustData, EmptyData, 'INSERT'
      FROM Inserted
      WHERE ITEMTYPE = 2

When you create three separate triggers, just replace the 'INSERT' value for Action with 'Update' and 'Delete' in those other triggers.

What I have trouble with is:

• what columns from Item should be stored into what column in MergeData ?
• your columns in Item or mostly INT – your columns in MergeData are Varchar – what kind of “conversion” do you want to apply here?

For more details, see the excellent SQL Server Books Online documentation (freely available!) on CREATE TRIGGER