sql语句删除重复记录(oracle)

1. select?*?from?login?a ??
2. ?where?rowid!=(select?min(rowid)?from?login?b?where?a.username=b.username) ??
3. ? ??
4. ?delete?from?login?a ??
5. ??where?rowid!=(select?max(rowid)?from?login?b?where?a.username=b.username)??