###查询重复记录
select * from my_tab where dup_col in(select dup_col from my_tab group by dup_col having count(dup_col)>1) order by dup_col;###查询重复记录（多个条件）
select * from my_tab as t1 where ( select count(*) from my_tab t2 where t2.col_1=t1.col_1 and t2.col_2=t1.col_2 and t2.col_3=t1.col_3 and t2.col_4=t1.col_4 )>1;###删除重复记录（只留一条） PG：使用ctid
delete from my_tab where dup_col in (select dup_col from my_tab group by dup_col having count(dup_col) > 1) and ctid not in (select min(ctid) from my_tab group by dup_col having count(dup_col)>1); delete from table_1 where (col_1,col_2,col_3) in (select col_1,col_2,col_3 from table_1 group by col_1,col_2,col_3 having count(*) > 1) and ctid not in (select min(ctid) from table_1 group by col_1,col_2,col_3 having count(*)>1);ORACLE：使用rowid
delete from my_tab where dup_col in (select dup_col from my_tab group by dup_col having count(dup_col) > 1) and rowid not in (select min(rowid) from my_tab group by dup_col having count(dup_col)>1);