- CREATE TABLE ... SELECT drops constraints for columns that
  are both in the create and select part.
  - Fixed by copying the constraint in
    Column_definiton::redefine_stage1_common()
- If one has both a default expression and check constraint for a
  column, one can get the error "Expression for field `a` is refering
  to uninitialized field `a`.
  - Fixed by ignoring default expressions for current column when checking
    for CHECK constraint