{ SET UNUSED { COLUMN column | ( column [, column]... )
[{ CASCADE CONSTRAINTS | INVALIDATE } [ CASCADE CONSTRAINTS | INVALIDATE ]...]
| DROP { COLUMN column | ( column [, column]... ) }
[{ CASCADE CONSTRAINTS | INVALIDATE } [ CASCADE CONSTRAINTS | INVALIDATE ]...]
[CHECKPOINT integer]
| DROP { UNUSED COLUMNS | COLUMNS CONTINUE } [CHECKPOINT integer]
}For information on the symbols and conventions of Backus-Naur Form (BNF) syntax, see Appendix A.