（這段是原創的）spa
今天心血來潮，針對前幾天韓哥說的一個會員只能建立一個商鋪的問題整理一下tab_shop_info這張表，而後準備刪掉會員id(cust_id)重複的項，並且只留下重複項裏面id(shop_id)最小的項。class
T_T 原本覺得兩三行寫完的東西，真正寫起來竟然這麼複雜------趕忙趕忙記下來！select
第一步：查詢重複項；統計
select cust_id from tab_shop_info group by cust_id having count(cust_id) > 1查詢
第二步：查詢重複項裏面shop_id最小的；tab
select min(shop_id) from tab_shop_info where cust_id in (di
select cust_id from tab_shop_info group by cust_id having count(cust_id) > 1vi
)co
第三步：統計全部重複項的shop_id；let
select shop_id from tab_shop_info where cust_id in (
select cust_id from tab_shop_info group by cust_id having count(cust_id) > 1
)
第四步：排除掉shop_id最小的那個；
select shop_if from (
select shop_id from tab_shop_info where cust_id in (
select cust_id from tab_shop_info group by cust_id having count(cust_id) > 1
)
)where shop_id not in(
select min(shop_id) from tab_shop_info where cust_id in (
select cust_id from tab_shop_info group by cust_id having count(cust_id) > 1
)
)
第五步：刪除
delete from tab_shop_info where shop_id in(
select shop_if from (
select shop_id from tab_shop_info where cust_id in (
select cust_id from tab_shop_info group by cust_id having count(cust_id) > 1
)
)where shop_id not in(
select min(shop_id) from tab_shop_info where cust_id in (
select cust_id from tab_shop_info group by cust_id having count(cust_id) > 1
)
)
)
OK,這樣纔算完工了！
可是總以爲這麼寫好複雜啊，若是有誰寫過簡單一些的寫法，麻煩在下面留言告知一下哈。1+1>=2，謝謝啦！