mysql 查询表中字段值相同的记录

[xingfuxiangyi]

test_id test_context
1 A
2 B
5 O
3 J
5 K
3 C
5 O
如上方，是一张表，我要怎么写查询语句选出test_id有重复的记录且test_context不同的记录要保留，剔除test_id无重复和test_id重复且test_context相同的记录。查询结果如：
test_id test_context
3 C
3 J
5 K
5 O
查询语句怎么写呢？表的记录有35多万条，考虑高效。有大神能帮忙吗？重赏

[rucypli]

select distinct * from tb A where exists(select 1 from tb B where A.id=B.id and A.content<>B.content)

[wwwwb]

SELECT distinct * from ttk a where exists(select 1 from ttk where a.test_id=test_id and a.test_context<>test_context )

[CT_LXL]

 select distinct t1.* from t1,(select test_id from t1 group by test_id having count(distinct test_context)>1) t2 where t1.test_id=t2.test_id order by test_id;

[ACMAIN_CHM]

select * from 是一张表 group by test_id,test_context