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，查出最新的数据

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 );