場景:
給予一張商品售賣表,表中數據爲商品的售賣記錄,假設表中數據是定時腳本插入的,每一個時間段的商品售賣數量不一樣,根據此表找各個商品的最多售賣數量的數據。
一、數據表html
CREATE TABLE `goods_sell` ( `id` int(11) NOT NULL AUTO_INCREMENT, `goods_id` int(10) unsigned NOT NULL DEFAULT '0', `sell_num` int(10) unsigned NOT NULL DEFAULT '0', `create_time` int(10) unsigned NOT NULL DEFAULT '0', PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
二、數據內容mysql
mysql> select * from goods_sell; +----+----------+----------+-------------+ | id | goods_id | sell_num | create_time | +----+----------+----------+-------------+ | 1 | 1 | 5 | 1420520010 | | 2 | 2 | 10 | 1420520000 | | 3 | 1 | 10 | 1410520000 | | 4 | 1 | 5 | 1510520000 | | 5 | 2 | 6 | 1510521000 | | 6 | 3 | 15 | 1510621000 | +----+----------+----------+-------------+ 6 rows in set (0.00 sec)
剖析其要求,也就是說,要用1條sql
找出goods_id 爲1 的id爲4的數據
找出goods_id 爲2 的id爲2的數據
找出goods_id 爲3 的id爲6的數據sql
三、怎麼作呢?
這時就能夠用MySQL的分組聚合,GROUP_CONCAT和SUBSTRING_INDEX一塊兒使用。
#查找各個商品售賣最多的一條記錄,此時group_concat()中必定要order by排序。要否則截取第一個數據就不對了。ide
select id,goods_id, SUBSTRING_INDEX(GROUP_CONCAT(sell_num order by sell_num desc),',',1) sell_num_max, create_time from goods_sell group by goods_id order by create_time DESC; +----+----------+--------------+-------------+ | id | goods_id | sell_num_max | create_time | +----+----------+--------------+-------------+ | 6 | 3 | 15 | 1510621000 | | 1 | 1 | 10 | 1420520010 | | 2 | 2 | 10 | 1420520000 | +----+----------+--------------+-------------+ 3 rows in set (0.00 sec)
不使用SUBSTRING_INDEX的話,查出來的數據是:spa
select id,goods_id, GROUP_CONCAT(sell_num order by sell_num desc) sell_num_list, create_time from good;
+----+----------+---------------+-------------+
| id | goods_id | sell_num_list | create_time |
+----+----------+---------------+-------------+
| 6 | 3 | 15 | 1510621000 |
| 1 | 1 | 10,5,5 | 1420520010 |
| 2 | 2 | 10,6 | 1420520000 |
+----+----------+---------------+-------------+
3 rows in set (0.00 sec)
因此用SUBSTRING_INDEX截取最前面的一個數據。
.net
文檔參考:
http://www.javashuo.com/article/p-ktqwnsme-ck.html
http://www.javashuo.com/article/p-zrgyqejy-hy.html
https://baijiahao.baidu.com/s?id=1595349117525189591&wfr=spider&for=pccode