NULL
s in NOT NULL
columns
NULL
s can exist in NOT NULL
columns in the following situations:
-
If you add a
NOT NULL
column to a populated table, the fields in the newly added column will all beNULL
. -
If you make an existing column
NOT NULL
, anyNULL
s already present in the column will remain in that state.
Firebird allows these NULL
s to stay, also backs them up, but refuses to restore them with gbak
.See [nullguide-add-not-null-field] and [nullguide-make-column-not-null].