MySQL入门教程之常用查询语句
示例数据库：
CREATE TABLE shop (
article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL,
dealer CHAR(20) DEFAULT '' NOT NULL,
price DOUBLE(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);
mysql> SELECT * FROM shop;
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0001 | A | 3.45 |
| 0001 | B | 3.99 |
| 0002 | A | 10.99 |
| 0003 | B | 1.45 |
| 0003 | C | 1.69 |
| 0003 | D | 1.25 |
| 0004 | D | 19.95 |
+---------+--------+-------+
1. 列最大值
最大的物品号是什么？
SELECT MAX(article) FROM shop;
2. 拥有某个列的最大值的行
找出最贵物品的编号、销售商和价格？
SELECT article, dealer, price FROM shop WHERE price=(SELECT MAX(price) FROM shop);另一个解决方案是按价格降序排序所有行并用MySQL特定LIMIT子句只得到第一行：
SELECT article, dealer, price FROM shop ORDER BY price DESC LIMIT 1;3. 列的最大值：按组每项物品的的最高价格是多少？SELECT article, MAX(price) AS price
FROM shop
GROUP BY article
+---------+-------+
| article | price |
+---------+-------+
| 0001 | 3.99 |
| 0002 | 10.99 |
| 0003 | 1.69 |
| 0004 | 19.95 |
+---------+-------+
4. 拥有某个字段的组间最大值的行对每项物品，找出最贵价格的物品的经销商？SELECT article, dealer, price
FROM shop s1
WHERE price=(SELECT MAX(s2.price)
FROM shop s2
WHERE s1.article = s2.article);
5. 使用用户变量找出价格最高或最低的物品的？
mysql> SELECT @min_price:=MIN(price),@max_price:=MAX(price) FROM shop;
mysql> SELECT * FROM shop WHERE price=@min_price OR price=@max_price;
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0003 | D | 1.25 |
| 0004 | D | 19.95 |
+---------+--------+-------+
6. 根据两个键搜索寻找两个通过OR组合到一起的关键字：
SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1' OR field2_index = '1'
还可以使用UNION将两个单独的SELECT语句的输出合成到一起:
SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1'UNIONSELECT field1_index, field2_index FROM test_table WHERE field2_index = '1';
