SQL语法以及语句的基本用法（2）

1. SQL SELECT TOP （前几）

mysql> SELECT * FROM Websites;
+----+---------------+---------------------------+-------+---------+
| id | name          | url                       | alexa | country |
+----+---------------+---------------------------+-------+---------+
|  1 | Google        | https://www.google.cm/    |     1 | USA     |
|  2 | 淘宝          | https://www.taobao.com/   |    13 | CN      |
|  3 | 阿里云大学      | http://edu.aliyun.com/    |  5000 | USA     |
|  4 | 微博           | http://weibo.com/         |    20 | CN      |
|  5 | Facebook      | https://www.facebook.com/ |     3 | USA     |
|  7 | stackoverflow | http://stackoverflow.com/ |     0 | IND     |
+----+---------------+---------------------------+-------+---------+

SELECT * FROM Websites LIMIT 2;

2. SQL LIKE 操作符（类似的）

SELECT * FROM Websites WHERE name LIKE 'G%';"%" 符号用于在模式的前后定义通配符（缺省字母）

3. SQL 通配符（搜索）

通配符	描述
%	替代 0 个或多个字符
_	替代一个字符
[charlist]	字符列中的任何单一字符
[^charlist] 或 [!charlist]	不在字符列中的任何单一字符

SELECT * FROM Websites WHERE name REGEXP '^[A-H]';//选取 name 以 A 到 H 字母开头的网站：

4. IN 操作符（多个值）

SELECT * FROM Websites WHERE name IN ('Google','菜鸟教程');

5. SQL BETWEEN 操作符（范围）

SELECT * FROM Websites WHERE alexa BETWEEN 1 AND 20;

6. SQL 别名（指定名称）

mysql> SELECT * FROM access_log;
+-----+---------+-------+------------+
| aid | site_id | count | date |
+-----+---------+-------+------------+
|   1 |       1 |    45 | 2016-05-10 |
|   2 |       3 |   100 | 2016-05-13 |
|   3 |       1 |   230 | 2016-05-14 |
|   4 |       2 |    10 | 2016-05-14 |
|   5 |       5 |   205 | 2016-05-14 |
|   6 |       4 |    13 | 2016-05-15 |
|   7 |       3 |   220 | 2016-05-15 |
|   8 |       5 |   545 | 2016-05-16 |
|   9 |       3 |   201 | 2016-05-17 |

SELECT w.name, w.url, a.count, a.date 
FROM Websites AS w, access_log AS a 
WHERE a.site_id=w.id and w.name=“菜鸟教程";

7. SQL FULL OUTER JOIN 语法（是否交叉）

SELECT column_name(s)
FROM table1
FULL OUTER JOIN table2
ON table1.column_name=table2.column_name;

8. SQL UNION 操作符（合并）

mysql> SELECT * FROM Websites;
+----+--------------+---------------------------+-------+---------+
| id | name         | url    | alexa | country |
+----+--------------+---------------------------+-------+---------+
| 1  | Google       | https://www.google.cm/    | 1     | USA     |
| 2  | 淘宝          | https://www.taobao.com/   | 13    | CN      |
| 3  | 阿里云大学      | http://edu.aliyun.com/    | 4689  | CN      |
| 4  | 微博          | http://weibo.com/         | 20    | CN   |
| 5  | Facebook     | https://www.facebook.com/ | 3     | USA     |
| 7  | stackoverflow | http://stackoverflow.com/ |   0 | IND     |
+----+---------------+---------------------------+-------+---------+

mysql> SELECT * FROM apps;
+----+------------+-------------------------+---------+
| id | app_name   | url | country |
+----+------------+-------------------------+---------+
|  1 | QQ APP | http://im.qq.com/  | CN  |
|  2 | 微博 APP | http://weibo.com/ | CN |
|  3 | 淘宝 APP | https://www.taobao.com/ | CN |
+----+------------+-------------------------+---------+
3 rows in set (0.00 sec)

实例
SELECT country FROM Websites
UNION
SELECT country FROM apps
ORDER BY country;

9. SQL SELECT INTO 语句（复制列插入新表）

只复制中国的网站插入到新表中
SELECT *
INTO WebsitesBackup2016
FROM Websites
WHERE country='CN';

10. SQL INSERT INTO SELECT 语句（复制数据插入旧表）

INSERT INTO table2
SELECT * FROM table1;