求一sql语句

原来表A有号码80条，然后又导入了30条，然后共有110条，但是其中重复的数据有20条，要把这后面导入的30条中的20条删除掉，要怎么写SQL？ORacle数据库，急，谢谢

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请提供表结构。

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id,card_num,ins_time

card_num重复了

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id,ins_time都不重复吧？

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SQL code:

delete from 表名 where ins_time not in(select ins_time from(select card_num,min(ins_time) ins_time from 表名 group by card_num));

SQL> select * from test;

T1 T2 T3
-------------------- -------------------- ----------
A A 1
A A 2
B A 3
C B 4
D B 5

SQL> select t2,min(t3) from test group by t2;

T2 MIN(T3)
-------------------- ----------
A 1
B 4


SQL> delete from test where t3 not in(select t3 from(select t2,min(t3) t3 from test group by t2));

已删除3行。

SQL> commit;

提交完成。

SQL> select * from test;

T1 T2 T3
-------------------- -------------------- ----------
A A 1
C