在Mysql中，要想删除一个表中重复的数据，并且只保留一条，该如何做？

例如，库中存在表t_invest_return_record_sum (t)，

有字段id，partner_id，invest_return_time，product_id ，有如下几条记录

（1,‘b’,'c','d'）,（2,‘b’,'c','d'），（5,‘b1’,'c1','d1'）

现要根据b,c,d三个字段重复的删除，留下id最小的一条（最多只有两条重复）

DELETE ta FROM t as ta INNER JOIN (SELECT max(tt.id) id FROM t as tt

GROUP BY tt.b,tt.c,tt.d HAVING COUNT(1)>=2) tb ON ta.id = tb.id;

不能直接删除，如

DELETE FROM t where id in (SELECT id FROM t as tt

GROUP BY tt.b,tt.c,tt.d HAVING COUNT(1)>=2)；

如果重复数超过2个或者不确定重复数，则需要在子查询中处理一下

（1,‘b’,'c','d'）,（2,‘b’,'c','d'），（3,‘b’,'c','d'）,（4,‘b’,'c','d'）,（5,‘b1’,'c1','d1'）

保留id最小的那条

DELETE tt FROM t_invest_return_record_sum tt INNER JOIN

(SELECT a.id FROM t_invest_return_record_sum a INNER JOIN (SELECT t.partner_id,t.invest_return_time,t.product_id FROM t_invest_return_record_sum t  GROUP BY t.partner_id,t.invest_return_time,t.product_id HAVING COUNT(1)>=2)t1 ON a.partner_id = t1.partner_id AND a.invest_return_time = t1.invest_return_time AND a.product_id = t1.product_id) t2 ON tt.id = t2.id LEFT JOIN  (SELECT min(a.id) id FROM t_invest_return_record_sum a INNER JOIN (SELECT t.partner_id,t.invest_return_time,t.product_id FROM t_invest_return_record_sum t  GROUP BY t.partner_id,t.invest_return_time,t.product_id HAVING COUNT(1)>=2)t1 ON a.partner_id = t1.partner_id AND a.invest_return_time = t1.invest_return_time AND a.product_id = t1.product_id) t3 ON tt.id = t3.id WHERE t3.id IS NULL