sql案例：删除多条内容相同的数据，只保留一条

在面试中遇到的一个问题

create table t_delete_test (id number primary key,name varchar(20));

insert into t_delete_test (id,name) values(1,'a');
insert into t_delete_test (id,name) values(2,'b');
insert into t_delete_test (id,name) values(3,'b');
insert into t_delete_test (id,name) values(4,'a');
insert into t_delete_test (id,name) values(5,'c');
insert into t_delete_test (id,name) values(6,'c');
insert into t_delete_test (id,name) values(7,'d');

select * from t_delete_test;

        ID NAME

---------- --------------------

         1 a

         2 b

         3 b

         4 a

         5 c

         6 c

 7 d

delete from t_delete_test t1 where
t1.name in (select t2.name from t_delete_test t2 group by t2.name having count(1)>1)
and 
t1.id not in(select min(t3.id) from t_delete_test t3 group by t3.name having count(1)>1);

备注：

select t2.name from t_delete_test t2 group by t2.name having count(1)>1 //查询名字至少有一条相同的数据

select min(t3.id) from t_delete_test t3 group by t3.name having count(1)>1 //查询名字至少有一条的数据，并且只显示最小的主键号