When changing columns from NULL to NOT NULL, or from NOT NULL to NULL, refer to the following table:
| Column Attribute | Composite Changes |
|---|---|
| NULL | Not permitted. |
| NOT NULL | Permitted. |
The following rules define how columns defined with NULL or NOT NULL attributes can be altered:
| This column type … | When defined as … | Can be altered to this column type … |
|---|---|---|
| Indexed | NULL | NULL only |
| NOT NULL | NOT NULL only | |
| Unindexed | NULL | NOT NULL If and only if the column does not contain nulls. |
| NOT NULL | NULL |