MySQL常用查询
建库建表准备环境
create database shop;
use shop;
CREATE TABLE shop (
article INT UNSIGNED DEFAULT '0000' NOT NULL,
dealer CHAR(20) DEFAULT '' NOT NULL,
price DECIMAL(16,2) DEFAULT '0.00' NOT NULL,
PRIMARY KEY(article, dealer));
INSERT INTO shop VALUES
(1,'A',3.45),(1,'B',3.99),(2,'A',10.99),(3,'B',1.45),
(3,'C',1.69),(3,'D',1.25),(4,'D',19.95);查看表数据
select max(article) as article from shop;
+---------+
| article |
+---------+
| 4 |
+---------+运用子查询
select article,dealer,price from shop where price = (select max(price) from shop);
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 4 | D | 19.95 |
+---------+--------+-------+查询每组的最大值
select article,max(price) as price from shop group by article;
+---------+-------+
| article | price |
+---------+-------+
| 1 | 3.99 |
| 2 | 10.99 |
| 3 | 1.69 |
| 4 | 19.95 |
+---------+-------+查找最贵的商品所在的行
方法一：
select article,dealer,price from shop where price = (select max(price) from shop);
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 4 | D | 19.95 |
+---------+--------+-------+
先找出price列中的最大值，在从表中寻找这个最大值所在的行
方法二：
select * from shop order by price desc limit 1;
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 4 | D | 19.95 |
+---------+--------+-------+
将整个shop表降序，取第一行，但这种方法的问题在于，只能取第一行，无法显示所有价值为19.95的商品可以使用用户自定义的变量来实现同时显示最高价与最低价
select @min_price:=min(price),@max_price:=max(price) from shop;
+------------------------+------------------------+
| @min_price:=min(price) | @max_price:=max(price) |
+------------------------+------------------------+
| 1.25 | 19.95 |
+------------------------+------------------------+
mysql> select * from shop where price=@min_price or price=@max_price;
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 3 | D | 1.25 |
| 4 | D | 19.95 |
+---------+--------+-------+