How to Create a DML AFTER trigger

Question

Hi Friends,
I need a help from you.
THe Scenario is We have Tables like parent and Child Table.
Like we have Child Table as  Name AcademyContacts,In that we have Columns like 
Guid(PK)Not Null,
AcademyId(FK), Not Null,
Name,Null
WorkPhone,Null
CellPhone,Null
Email Id,Null
Other.Null
Since we have given Null to ''Workphone'',''Cellphone '', ''Email ID''.when inserting the data into these table 
if the particular columns are empty while inserting also the data will get populate into the table.And
I need is if these columns are ''Workphone'',''Cellphone'' , ''Email ID''  they cant insert the data into table.
Like it must trigger like ''Please enter atleast one of these ''Workphone'',''Cellphone'' , ''Email ID'' columns.
How to do this in triggers please suggests me friends !!!!
I am waiting for your response !!!
Arunraj Kumar

Answer 1

Respecting all i would suggest it is not manager who decide which is right or wrong. Business should decide which is a good  solution. 
Trigger also use for business validation and you can put this validation is Stored procedure also.
Question is how are you inserting  data to parent table , whether your parent  and child table are in within same transaction or not . Other wise if you insert data to parent and while inserting to child table you throw this message it will not
be consistent and   where you want to show this message . You have to consider all these scenarios.
If you use Stored procedure you can return your message. Or It is advisable if you have a front end better handle this in front end.
For your scenario if you want to go for trigger , for you , you need to implement Instead of DML trigger.
Example :
CREATE TRIGGER IO_Trig_INS_Child ON ChildTable
INSTEAD OF INSERT
AS
BEGIN
SET NOCOUNT ON;
IF NOT EXISTS( SELECT * FROM Inserted I where I.Workphone IS NOT NULL OR I.Cellphone IS NOT NULL OR I.EmailID IS NOT NULL)
THROW; -- Refer http://msdn.microsoft.com/en-IN/library/ee677615.aspx for detail use of throw
END
Create storedprocedure InsertSp
AS
Begin Try 
Begin Tran 
Insert into parenttable values ( <<your values>>)
--If you want to handle in sp , here you can check the column value and throw error befor inserting to child
Insert into child table values (<<>>) 
Commit
END Try 
Begin Catch 
THROW 'Your message'
End Catch 
Sandip Pani http://SQLCommitted.com