mysql清除重复数据，只保留一条最新记录

1，查出重复数据，现以card_number 重复就认定为重复

SELECT card_number FROM crm_def_customer GROUP BY card_number HAVING count(card_number) > 1

2，查出重复中最新的数据，以create_date字段为标识

SELECT max(create_date) FROM crm_def_customer GROUP BY card_number HAVING count(card_number) > 1

3,组合查出重复数据排除最新记录在外

 SELECT id from (
        SELECT id,card_number FROM crm_def_customer WHERE card_number in(
            SELECT card_number FROM crm_def_customer GROUP BY card_number HAVING count(card_number) > 1)
            AND create_date  not IN(SELECT min(create_date) FROM crm_def_customer GROUP BY card_number HAVING count(card_number) > 1)) as t 

//删除前也可查出name等更多项确保sql语句正确

4，作删除

DELETE  from   crm_def_customer where id in(
 SELECT id from (
        SELECT id,card_number FROM crm_def_customer WHERE card_number in(
            SELECT card_number FROM crm_def_customer GROUP BY card_number HAVING count(card_number) > 1)
            AND create_date  not IN(SELECT min(create_date) FROM crm_def_customer GROUP BY card_number HAVING count(card_number) > 1)
 ) as t );

根据两个字段去重 GROUP BY 两个字段 count(*)，其它思路同上

SELECT house_name,field3 from res_house GROUP BY field3 ,house_name HAVING count(*) > 1