mysql 怎樣先排序再分組

權遊遊牧族：衆所周知！一句SqL語句不能先排序再分組。因此這裏給出幾個案例

--表結構--
create table `shop` (
    `id` int (10) PRIMARY KEY,
    `shop_name` varchar (100),
    `item_name` varchar (100),
    `price` int (10)
); 

insert into `shop` (`id`, `shop_name`, `item_name`,`price`) values('1','小賣部','醬油','12');
insert into `shop` (`id`, `shop_name`, `item_name`,`price`) values('2','小賣部','醋','15');
insert into `shop` (`id`, `shop_name`, `item_name`,`price`) values('3','小賣部','脈動','20');
insert into `shop` (`id`, `shop_name`, `item_name`,`price`) values('4','小賣部','沙姜','2');
insert into `shop` (`id`, `shop_name`, `item_name`,`price`) values('5','超市','豬肉','24');
insert into `shop` (`id`, `shop_name`, `item_name`,`price`) values('6','超市','生菜','6');
insert into `shop` (`id`, `shop_name`, `item_name`,`price`) values('7','超市','菜心','5');
insert into `shop` (`id`, `shop_name`, `item_name`,`price`) values('8','連鎖店','生薑','3');
insert into `shop` (`id`, `shop_name`, `item_name`,`price`) values('9','超市','牛肉','30');
insert into `shop` (`id`, `shop_name`, `item_name`,`price`) values('10','連鎖店','蒜頭','2');
insert into `shop` (`id`, `shop_name`, `item_name`,`price`) values('11','連鎖店','黃瓜','20');

對價格price進行排序而後再根據商店類型shop_name進行分組查詢

select * from (select * from shop order by price desc) a GROUP BY a.shop_name

結果只是按照表數據的順序，簡單地進行了分組查詢操做，可是這時候咱們還不能下結論說這條sql就是錯誤的，咱們用另外一個數據庫版本（MySql 5.5.57）測試一下。

最後放上相應的解決辦法：

-方法一，僅適用於低於5.7版本的MySql--
select * from (select * from shop order by price desc) a GROUP BY a.shop_name; 

--方法二--
select * from (select * from shop order by price desc limit 999999) a GROUP BY a.shop_name;

--方法三--
select * from shop a where N > (select count(*) from shop b where b.shop_name = a.shop_name and a.price < b.price) order by a.shop_name,a.price desc;

PS:方法二中使用limit，須要limit的範圍足夠大能包括全部數據，而且每種分類只會顯示一條數據，可是數據較多時運行效率要比方法三快上不少，方法三可以控制每種分類顯示多少條數據，把N換成須要顯示對應的數字便可。

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