如下：
DELETE FROM categories a WHERE ( a.id, a.name, a.parent_id ) IN ( SELECT id, name, parent_id FROM categories GROUP BY id, name, parent_id HAVING count( * ) > 1 ) AND ctid NOT IN ( SELECT min(ctid) FROM categories GROUP BY id, name, parent_id HAVING count( * ) > 1 )
关键点：oracle中有内部id为rowid, 在postgresql中有ctid.
参照：oracle rowid and postgresql ctid
原文：https://www.cnblogs.com/legendjslc/p/11785669.html