Several years ago I wrote a series of 8 posts about constraint creation optimization. I think it’s time to add some more posts to the series.
I showed there, among other things, that Oracle does a nice optimization – that may save plenty of time – when we add in a single ALTER TABLE statement a new (nullable with no default value) column and a corresponding:
– inline (a.k.a. “column-level”) check constraint
or
– foreign key constraint (either inline or out-of-line)
What about NOT NULL constraints?
Oracle has a special optimization for the case of adding a column with a NOT NULL constraint (and no default value).
It checks if the table contains at least one record. If it does, then we cannot add the new column, becuase the NOT NULL constraint will be violated for all the existing rows. If the table doesn’t contain any records, the new column can be added.
Let’s start with an empty table: Continue reading “Optimization of NOT NULL Constraint Creation”