MySQL 常用查询

2011-3-29 Jerry MySQL

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'
UNION
SELECT field1_index, field2_index
    FROM test_table WHERE field2_index = '1';

标签: MySQL


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