Question

I have an asp.net web app where a user can update a table in a database. I would like to know the proper method of doing this. As you can see in the image below, the red shaded area is the data that I have in common that I do not need to update.

Here are the steps that I need to take:

1. Don’t update data if it exists
2. Delete data that is not in the user update
3. Add data from the user update that is not already in the table

I need to audit this table also, so I will have a trigger on it. I would like to know in theory what is the best way to do this kind of update to a table?

thank you to Aaron who introduced the concept of merge.

Here is what the table data looks like:

foreignkey  model  primarykey
1            AA       1
1            AA1      2
1            AA3      3
23           B        4
22           C        5

The user will be adding data that looks like this:

foreignkey  model  primarykey
1            A1       1
1            AA1      2
1            AA3      3
22           C        5

As you can see, the first row was updated, and the second to last row was deleted entirely. Can you please help me with this merge statement?

Answer 1

Yes, it’s possible and it’s called a merge. See the documentation for the SQL Server MERGE Statement.

If you don’t want to perform any updates if the data already exists, then just don’t add a WHEN MATCHED clause. USE WHEN NOT MATCHED BY SOURCE and WHEN NOT MATCHED BY TARGET to insert/delete the missing/removed rows.