1、查询表中某字段值，如查询学生表中姓名=hapasm

select * from student where nam='hapasm'

2、查询物料表中，查询出所有物料代码重复的数据

select * from t_gd_material a where  (a.material_sn) in (select material_sn from t_gd_material GROUP BY material_sn having count(*)>1)

3、查询出所有数据进行分组之后，和重复数据的重复次数的查询数据，先列下：

4、查找表中多余的重复记录，重复记录是根据单个字段（protocol_detail_id ）来判断，并降序排列

select * from t_ex_order_detail where protocol_detail_id in (select protocol_detail_id from t_ex_order_detail group by protocol_detail_id having count(protocol_detail_id) > 1)order by protocol_detail_id desc

5、删除表中多余的重复记录，重复记录是根据单个字段（protocol_detail_id）来判断，只留有rowid最小的记录

delete from t_ex_order_detail where protocol_detail_id in (select protocol_detail_id from t_ex_order_detail group by protocol_detail_id having count(protocol_detail_id) > 1)and rowid not in (select min(rowid) from t_ex_order_detail group by protocol_detail_id having count(protocol_detail_id )>1)

6、查找表中多余的重复记录（多个字段）

select * from t_ex_order_detail a where (a.protocol_detail_id,a.id) in (select protocol_detail_id,id from t_ex_order_detail GROUP BY protocol_detail_id,id HAVING count(*)>1)

7、查询重复

select id,protocol_detail_id from t_gd_goods where protocol_detail_id in (select protocol_detail_id  from t_gd_goods group by protocol_detail_id having count(protocol_detail_id)>1)