doc/src/sgml/ref/drop_group.sgml

doc/src/sgml/ref/drop_role.sgml

doc/src/sgml/ref/drop_user.sgml

src/backend/commands/user.c

src/backend/nodes/copyfuncs.c

src/backend/nodes/equalfuncs.c

src/backend/parser/gram.y

src/include/nodes/parsenodes.h

src/test/regress/expected/drop_if_exists.out

src/test/regress/sql/drop_if_exists.sql