Very few databases support transactional DDL, meaning that you can do something like:

  BEGIN;
  DROP TABLE foo;
  CREATE TABLE bar (t int);
  ROLLBACK;

...and it will just work as you expect. Oracle doesn't, nor does MSSQL.

As far as I know, other than Postgres, only Sybase ASE, Informix, DB2 UDB, and Firebird support transaction DDL.