MySQL查询和去重记录

查询MySQL中重复的数据，一下字段表示的含义是：
查询test表中，gd_id 重复的字段
select * from test a where (a.gd_id) in (select gd_id from test group by gd_id having count(*) > 1)
去重MySQL中的数据
DELETE FROM xz_nursery_all
WHERE gd_id in
(
SELECT gd_id FROM
(
SELECT gd_id FROM xz_nursery_all GROUP BY gd_id HAVING count(gd_id)>1
) t1
)
AND id NOT IN
(
SELECT id FROM
(
SELECT min(id) id FROM xz_nursery_all GROUP BY gd_id HAVING count(gd_id)>1
) t2
)