T-SQL UPDATE statement affects more records than select statement

Question

The following is driving me nuts, please help me!

As a check before running an UPDATE statement (T-SQL; SQL Server 2012) I run:

select  * 
from Treatment_Day42 
where td42pinit = 'J M' and td42pid = 'ADA';

and I get 1 row returned, as I expect.

However, running

update Treatment_Day42 set td42pid = 'ADA252' 
where td42pinit = 'J M' and td42pid = 'ADA';

affects four records, not one as in the select statement with the exact same WHERE clause. I get the row returned by the select plus 3 other rows where td42pid = ADA458, ADA671 and ADA658.

Why is the UPDATE affecting more rows than I intend it to?

Thanks.

Clemens

Answer 1

A trigger on the table could do this. Have you checked for an existing trigger?