已有数据的表-建联合索引

清理重复数据，建立联合唯一索引

1. 查看重复数据

SELECT * FROM holiday_focamobilerel
WHERE (cardnumber, mobile) IN (SELECT cardnumber, mobile FROM holiday_focamobilerel GROUP BY cardnumber, mobile HAVING COUNT(1) > 1);

2. 删除重复数据

- 保留order_id and sub_order_id不为空的

- 如果order_id和sub_order_id都为空，保留id最大的

DELETE FROM holiday_focamobilerel h
WHERE (cardnumber, mobile) IN (SELECT cardnumber, mobile FROM holiday_focamobilerel GROUP BY cardnumber, mobile HAVING COUNT(1) > 1)
AND h.id NOT IN (select id from holiday_focamobilerel h where h.order_id  is not null  or h.sub_order_id  is not null )
and h.id not in (SELECT MAX(id) FROM holiday_focamobilerel GROUP BY cardnumber, mobile HAVING COUNT(1) > 1);

3. 建立联合唯一约束

alter table holiday_focamobilerel add constraint cardnumber_mobile_key unique("cardnumber","mobile")

原文地址：https://www.cnblogs.com/weihengblog/p/10320394.html