Question

I’ve added a history table to my database. Originally I added a Bit called Deleted and intended to update it to 1 if that row was ever deleted, otherwise each row is an update.

Then I was informed we need to log who deleted what when. So I added Nullable [DeletedBy] [DeletedOn] fields.
At this point I was wondering if this made my Deleted Bit redundant. You could simply query the table, checking where DeletedBy is not Null if you want to see which row is Deleted.

I intended to ask in this question which is better practice:

1. Having the extra Bit Column

2. Using the nullable columns that are already there, to Identify Deleted Rows

But I’m starting to think this is a preference thing. So instead my question is, which is more efficient? If this table gets massive, is there a performance gain to running:

    Select * from MyTable where [Deleted] = 1

over

    Select * from MyTable where [DeletedBy] is not null

Answer 1

This is more a preference. Technically the datetime field is larger than a bit field, but since you are required to store it anyway it does not really matter. However performance wise you can index either and get the same results. I personally think the bit field is redundant and use the nullable datetime.