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sql之检索方法

2019-01-15 14:42 423 查看

检索方法

select语句

无顺序检索：
检索单列：

输入▼

#从books表中检索名为author的列。

SELECT author FROM books;

输出▼

#查询单列的结果：

+----------------+
| author         |
+----------------+
| Pruitt, et al. |
| Michael Morgan |
| Thomas Down    |
| Thomas Schenk  |
+----------------+
检索多列：

输入▼

#从books表中检索名为author，title，price的三列。

SELECT author,title,price
FROM books;

输出▼

#查询多列的结果：

+----------------+---------------------------------------------------+-------+
| author         | title                                             | price |
+----------------+---------------------------------------------------+-------+
| Pruitt, et al. | Teach Yourself GIMP in 24 Hours                   | 24.99 |
| Michael Morgan | Java 2 for Professional Developers                | 34.99 |
| Thomas Down    | Installing Debian GNU/Linux                       | 24.99 |
| Thomas Schenk  | Caldera OpenLinux system Administration Unleashed | 49.99 |
+----------------+---------------------------------------------------+-------+
检索所有列：

使用通配符~

输入▼

#从books表中检索所有的列。

SELECT *
FROM books;

输出▼

#查询所有列的结果：

+---------------+----------------+---------------------------------------------------+-------+
| isbn          | author         | title                                             | price |
+---------------+----------------+---------------------------------------------------+-------+
| 0-672-31509-2 | Pruitt, et al. | Teach Yourself GIMP in 24 Hours                   | 24.99 |
| 0-672-31697-8 | Michael Morgan | Java 2 for Professional Developers                | 34.99 |
| 0-672-31745-1 | Thomas Down    | Installing Debian GNU/Linux                       | 24.99 |
| 0-672-31769-9 | Thomas Schenk  | Caldera OpenLinux system Administration Unleashed | 49.99 |
+---------------+----------------+---------------------------------------------------+-------+
检索不同的值：

不希望每个值每次都出现时使用的方法~

则使用关键字 DISTINCT 来让输出结果具有唯一性~

注意：DISTINCT关键字是作用于所有的列，只有所有选定列都相同时才会只显示一个。

  • 一般查看方法：

输入▼

#从persons表中检索ages列。

SELECT ages
FROM persons;

输出▼

#查询ages列的结果：

+------+
| ages |
+------+
|   18 |
|   18 |
|    8 |
|   19 |
|   45 |
|    8 |
+------+
  • 只显示一次的查看方法：

输入▼

#从persons表中检索ages列。

SELECT DISTINCT ages
FROM persons;

输出▼

#查询无重复ages列的结果：

+------+
| ages |
+------+
|   18 |
|    8 |
|   19 |
|   45 |
+------+
顺序检索：
顺序检索单列：
  • 无顺序查看方法：

输入▼

#从persons表中检索ages列。

SELECT ages
FROM persons;

输出▼

#无顺序查询ages列的结果：

+------+
| ages |
+------+
|   18 |
|   18 |
|    8 |
|   19 |
|   45 |
|    8 |
+------+
  • 顺序查看方法：

输入▼

#顺序从persons表中检索ages列。

SELECT ages
FROM persons
ORDER BY ages;

输出▼

#顺序查询ages列的结果：

+------+
| ages |
+------+
|    8 |
|    8 |
|   18 |
|   18 |
|   19 |
|   45 |
+------+
顺序检索多列：
  • 无顺序查看方法：

输入▼

#从persons表中检索ages列。

SELECT author,title,price
FROM books；

输出▼

#无顺序查询多列的结果：

+----------------+---------------------------------------------------+-------+
| author         | title                                             | price |
+----------------+---------------------------------------------------+-------+
| Pruitt, et al. | Teach Yourself GIMP in 24 Hours                   | 24.99 |
| Michael Morgan | Java 2 for Professional Developers                | 34.99 |
| Thomas Down    | Installing Debian GNU/Linux                       | 24.99 |
| Thomas Schenk  | Caldera OpenLinux system Administration Unleashed | 49.99 |
+----------------+---------------------------------------------------+-------+
  • 顺序查看方法：

输入▼

#顺序从books表中检索多列。

SELECT author,title,price
FROM books
ORDER BY title,price;

#将按照先title排序，title相同时再price的顺序输出/

输出▼

#顺序查询多列的结果：

+----------------+---------------------------------------------------+-------+
| author         | title                                             | price |
+----------------+---------------------------------------------------+-------+
| Thomas Schenk  | Caldera OpenLinux system Administration Unleashed | 49.99 |
| Thomas Down    | Installing Debian GNU/Linux                       | 24.99 |
| Michael Morgan | Java 2 for Professional Developers                | 34.99 |
| Pruitt, et al. | Teach Yourself GIMP in 24 Hours                   | 24.99 |
+----------------+---------------------------------------------------+-------+
按列位置排序：

不使用别名，使用按相对列位置进行排序~

  • 无顺序查看方法：

输入▼

#从persons表中检索ages列。

SELECT author,title,price
FROM books；

输出▼

#无顺序查询多列的结果：

+----------------+---------------------------------------------------+-------+
| author         | title                                             | price |
+----------------+---------------------------------------------------+-------+
| Pruitt, et al. | Teach Yourself GIMP in 24 Hours                   | 24.99 |
| Michael Morgan | Java 2 for Professional Developers                | 34.99 |
| Thomas Down    | Installing Debian GNU/Linux                       | 24.99 |
| Thomas Schenk  | Caldera OpenLinux system Administration Unleashed | 49.99 |
+----------------+---------------------------------------------------+-------+
  • 顺序查看方法：

输入▼

#顺序从books表中检索多列。

SELECT author,title,price
REOM books
ORDER BY 2,1;

#将按照先相对列为2进行排序，相对为2的列相同时再按相对列为1的顺序输出/

输出▼

#顺序查询多列的结果：

+----------------+---------------------------------------------------+-------+
| author         | title                                             | price |
+----------------+---------------------------------------------------+-------+
| Thomas Schenk  | Caldera OpenLinux system Administration Unleashed | 49.99 |
| Thomas Down    | Installing Debian GNU/Linux                       | 24.99 |
| Michael Morgan | Java 2 for Professional Developers                | 34.99 |
| Pruitt, et al. | Teach Yourself GIMP in 24 Hours                   | 24.99 |
+----------------+---------------------------------------------------+-------+
倒序排序：

使用关键字 DESC 实现相反的顺序（从大到小）排序输出

注意：对多个列进行降序排序时，必须对每一列都指定关键字 DESC ~

  • 无顺序查看方法：

输入▼

#从persons表中检索ages列。

SELECT author,title,price
FROM books；

输出▼

#无顺序查询多列的结果：

+----------------+---------------------------------------------------+-------+
| author         | title                                             | price |
+----------------+---------------------------------------------------+-------+
| Pruitt, et al. | Teach Yourself GIMP in 24 Hours                   | 24.99 |
| Michael Morgan | Java 2 for Professional Developers                | 34.99 |
| Thomas Down    | Installing Debian GNU/Linux                       | 24.99 |
| Thomas Schenk  | Caldera OpenLinux system Administration Unleashed | 49.99 |
+----------------+---------------------------------------------------+-------+
  • 倒序查看方法：

输入▼

#倒序从books表中检索多列。

SELECT author,title,price
REOM books
ORDER BY price DESC;

#按照price从大到小输出

输出▼

#顺序查询多列的结果：

+----------------+---------------------------------------------------+-------+
| author         | title                                             | price |
+----------------+---------------------------------------------------+-------+
| Thomas Schenk  | Caldera OpenLinux system Administration Unleashed | 49.99 |
| Michael Morgan | Java 2 for Professional Developers                | 34.99 |
| Pruitt, et al. | Teach Yourself GIMP in 24 Hours                   | 24.99 |
| Thomas Down    | Installing Debian GNU/Linux                       | 24.99 |
+----------------+---------------------------------------------------+-------+
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