MySQL学习笔记之三排序和过滤

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在数据库的使用中排序和过滤也是经常的操作

排序检索数据,关键字order

普通排序
mysql> select * from user;
+----+--------+-----+-----------------------+-----+
| id | name   | age | address               | sex |
+----+--------+-----+-----------------------+-----+
|  1 | 张三   |  20 | 北京海底市南区        |   1 |
|  2 | 李四   |  22 | 北京海底市南区        |   1 |
|  3 | 赵芸   |  32 | 上海市徐汇区          |   2 |
|  4 | 王丽   |  31 | 广州厦门              |   2 |
+----+--------+-----+-----------------------+-----+
4 rows in set (0.00 sec)
按照列名name排序是什么样呢？
mysql> select * from user order by name;
+----+--------+-----+-----------------------+-----+
| id | name   | age | address               | sex |
+----+--------+-----+-----------------------+-----+
|  1 | 张三   |  20 | 北京海底市南区        |   1 |
|  2 | 李四   |  22 | 北京海底市南区        |   1 |
|  4 | 王丽   |  31 | 广州厦门              |   2 |
|  3 | 赵芸   |  32 | 上海市徐汇区          |   2 |
+----+--------+-----+-----------------------+-----+
4 rows in set (0.00 sec)

mysql> select * from user order by name, age;
+----+--------+-----+-----------------------+-----+
| id | name   | age | address               | sex |
+----+--------+-----+-----------------------+-----+
|  1 | 张三   |  20 | 北京海底市南区        |   1 |
|  2 | 李四   |  22 | 北京海底市南区        |   1 |
|  4 | 王丽   |  31 | 广州厦门              |   2 |
|  3 | 赵芸   |  32 | 上海市徐汇区          |   2 |
+----+--------+-----+-----------------------+-----+
4 rows in set (0.00 sec)

使用关键字desc,可以改为降序排列
mysql> select * from user order by name desc;
+----+--------+-----+-----------------------+-----+
| id | name   | age | address               | sex |
+----+--------+-----+-----------------------+-----+
|  3 | 赵芸   |  32 | 上海市徐汇区          |   2 |
|  4 | 王丽   |  31 | 广州厦门              |   2 |
|  2 | 李四   |  22 | 北京海底市南区        |   1 |
|  1 | 张三   |  20 | 北京海底市南区        |   1 |
+----+--------+-----+-----------------------+-----+
4 rows in set (0.00 sec)

mysql> select * from user order by name limit 3;
+----+--------+-----+-----------------------+-----+
| id | name   | age | address               | sex |
+----+--------+-----+-----------------------+-----+
|  1 | 张三   |  20 | 北京海底市南区        |   1 |
|  2 | 李四   |  22 | 北京海底市南区        |   1 |
|  4 | 王丽   |  31 | 广州厦门              |   2 |
+----+--------+-----+-----------------------+-----+
3 rows in set (0.00 sec)

数据过滤，关键字where

mysql> select * from user where id = 2;
+----+--------+-----+-----------------------+-----+
| id | name   | age | address               | sex |
+----+--------+-----+-----------------------+-----+
|  2 | 李四   |  22 | 北京海底市南区        |   1 |
+----+--------+-----+-----------------------+-----+
1 row in set (0.00 sec)

和order by 配合使用
mysql> select * from user where id <4  order by name limit 3;
+----+--------+-----+-----------------------+-----+
| id | name   | age | address               | sex |
+----+--------+-----+-----------------------+-----+
|  1 | 张三   |  20 | 北京海底市南区        |   1 |
|  2 | 李四   |  22 | 北京海底市南区        |   1 |
|  3 | 赵芸   |  32 | 上海市徐汇区          |   2 |
+----+--------+-----+-----------------------+-----+
3 rows in set (0.00 sec)

关于where子句的位置: 在同时使用where和order by子句时候, 我们应该让order by位于where 子句之后。

mysql> select * from user where id between 2 and 4;
+----+--------+-----+-----------------------+-----+
| id | name   | age | address               | sex |
+----+--------+-----+-----------------------+-----+
|  2 | 李四   |  22 | 北京海底市南区        |   1 |
|  3 | 赵芸   |  32 | 上海市徐汇区          |   2 |
|  4 | 王丽   |  31 | 广州厦门              |   2 |
+----+--------+-----+-----------------------+-----+
3 rows in set (0.00 sec)

mysql> select * from user where id >1 and id < 4;
+----+--------+-----+-----------------------+-----+
| id | name   | age | address               | sex |
+----+--------+-----+-----------------------+-----+
|  2 | 李四   |  22 | 北京海底市南区        |   1 |
|  3 | 赵芸   |  32 | 上海市徐汇区          |   2 |
+----+--------+-----+-----------------------+-----+
2 rows in set (0.00 sec)

mysql> select * from user where id <2 or id >=3;
+----+--------+-----+-----------------------+-----+
| id | name   | age | address               | sex |
+----+--------+-----+-----------------------+-----+
|  1 | 张三   |  20 | 北京海底市南区        |   1 |
|  3 | 赵芸   |  32 | 上海市徐汇区          |   2 |
|  4 | 王丽   |  31 | 广州厦门              |   2 |
+----+--------+-----+-----------------------+-----+
3 rows in set (0.00 sec)

in操作符可以用于指定操作范围，范围内每个条件都可以进行匹配。
mysql> select * from user where name in ("张三","李四");
+----+--------+-----+-----------------------+-----+
| id | name   | age | address               | sex |
+----+--------+-----+-----------------------+-----+
|  1 | 张三   |  20 | 北京海底市南区        |   1 |
|  2 | 李四   |  22 | 北京海底市南区        |   1 |
+----+--------+-----+-----------------------+-----+
2 rows in set (0.00 sec)

in操作符的优势：
1. 使用长的合法选项清单时候, in操作符比较直观。
2. in操作符计算的次序比较好管理
3. in操作符一般比or操作符效率快
4. in操作符可以包括其他select语句，能够更加动态的创建where子句

not操作符只有一个特点, 就是否定它后面的任何条件。
mysql支持not对in, between, exists子句取反。

mysql> select * from user where name not in ("张三","李四");
+----+--------+-----+--------------------+-----+
| id | name   | age | address            | sex |
+----+--------+-----+--------------------+-----+
|  3 | 赵芸   |  32 | 上海市徐汇区       |   2 |
|  4 | 王丽   |  31 | 广州厦门           |   2 |
+----+--------+-----+--------------------+-----+
2 rows in set (0.00 sec)

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