How to set trigger based on update query in SQL Server? - sql-server

Question

I am trying to set trigger whenever phone is updated in table1 and then do operation like check phone from table2 and if present, pick up the employee code from table2 and then update employee code in table1.
My code for trigger:
CREATE TRIGGER UPDATED_Contact_Trigger
ON table1
AFTER UPDATE
AS
DECLARE #tuid bigint;
DECLARE #phone varchar(15);
DECLARE #employee_code varchar(10);
IF (UPDATE (phone)) --Phone is the Column Name
BEGIN
SELECT #employee_code = i.emp_code
FROM table2 i (nolock)
WHERE i.MOBILE_NO = #phone
UPDATE table1
SET client_code = #employee_code
WHERE tuid= #tuid
END;
This trigger is set, but there is no update on table1 even if I update a contact which is present in table2

Answer 1

You're not even looking at the Inserted or Deleted pseudo tables in your code - how do you want to know what rows have been updated??
Inserted is a pseudo table that contains all updated rows - and it contains the new values after the update operation, while Deleted contains the same rows, but with the old values before the update.
You need to do something like this:
join your Table1 to Inserted to get the rows that were updated (since you didn't show your table structure, I cannot know what your primary key on Table1 is - you need to use that to join to Inserted)
add a join to your Table2 and pick those rows that have been updated, and limit those to the ones that have been updated in the Phone column (by comparing the Inserted.Phone value to Deleted.Phone)
Try this code:
CREATE TRIGGER UPDATED_Contact_Trigger
ON table1
AFTER UPDATE
AS
BEGIN
-- update your base table
UPDATE t1
-- set the client_code to the employee_code from Table2
SET client_code = t2.employee_code
FROM dbo.Table1 t1
-- join to "Inserted" to know what rows were updated - use the primary key
INNER JOIN Inserted i ON t1.(primarykey) = i.(primarykey)
-- join to "Deleted" to check if the "Phone" has been updated (between Deleted and Inserted)
INNER JOIN Deleted d ON i.(primarykey) = d.(primarykey)
-- join to "Table2" to be able to fetch the employee_code
INNER JOIN dbo.Table2 t2 ON t2.mobile_no = t1.phone
-- ensure the "Phone" has changed, between the old values (Deleted) and new values (Inserted)
WHERE i.Phone <> d.Phone;
END;