How Dropping a Column Affects Constraints

When you drop a column, all constraints on that column are also dropped:

• All single-column constraints are dropped.
• All referential constraints that reference the column are dropped.
• All check constraints that reference the column are dropped.
• If the column is part of a multiple-column primary-key or unique constraint, the constraints placed on the multiple columns are also dropped. This action, in turn, triggers the dropping of all referential constraints that reference the multiple columns.

Because any constraints that are associated with a column are dropped when the column is dropped, the structure of other tables might also be altered when you use this clause. For example, if the dropped column is a unique or primary key that is referenced in other tables, those referential constraints also are dropped. Therefore the structure of those other tables is also altered.