刪除表中所有記錄只留下第一條,按照rownum排他,使用rowid刪除

先生成表中的rownum然後刪除rownum!=1的記錄

 delete from emp where rowid in 
 (
 select id  from
 (
 select e.rowid id,rownum r from emp e where ename='TOM' and rownum <=(select count(*) from emp e where ename='TOM')
 ) 
 where r != 1
 )