Why is my update affecting twice the number of records than expected?

Question

I have the following query:

update Table1
set id=2
where nbr in (select nbr from Other.dbo.table)

The "select nbr from Other.dbo.table" has 500 records. Yet when I run the update, it says I am updating 1,000 records. I have checked table1, and there are only 500 rows that match the filter.

select * from table1 where nbr in (select nbr from Other.dbo.table)

I tried changing the query to be a join and using a temp table to store the filter list, but I receive the same results.

Why am I updating 1000 records when only 500 match?

There is an update trigger on Table1.

Answer 1

An update trigger on table1 causes the UI to return double the amount of records. The 500 records are being updated. However, each update causes a new record to be inserted into an audit table. The UI returns the count of the total rows affected for the query statement, not just the update itself!