SQL WHERE语句

WHERE基础语法

SELECT * FROM table_name
WHERE id = 1;

SELECT title FROM table_name
WHERE id = 100;

WHERE + AND/OR

// 查询表中国家为中国或美国的数据集

SELECT * FROM table_name
WHERE country='CN'
OR country='USA';

// 查询表中国家是中国，且评分大于8.5的数据

SELECT * FROM table_name
WHERE country='CN'
AND rate>8.5;

// 查询评分大于8.5的中国或美国的电影数据

SELECT * FROM table_name
WHERE rate>8.5
AND (country='CN' OR country='USA');

WHERE + ORDER BY

ORDER BY 关键字用于对结果集按照一个列或者多个列进行排序。

ORDER BY 关键字默认按照升序对记录进行排序。如果需要按照降序对记录进行排序，您可以使用 DESC 关键字。

以菜鸟教程中SQL学习的Websites表为例

+----+--------------+---------------------------+-------+---------+
| id | name         | url                       | alexa | country |
+----+--------------+---------------------------+-------+---------+
| 1  | Google       | https://www.google.cm/    | 1     | USA     |
| 2  | 淘宝          | https://www.taobao.com/   | 13    | CN      |
| 3  | 菜鸟教程      | http://www.runoob.com/    | 4689  | CN      |
| 4  | 微博          | http://weibo.com/         | 20    | CN      |
| 5  | Facebook     | https://www.facebook.com/ | 3     | USA     |
+----+--------------+---------------------------+-------+---------+

ORDER BY

// 通过alexa升序排列

SELECT * FROM Websites
ORDER BY alexa;

ORDER BY ASC/DESC

// 通过alexa降序排列

SELECT * FROM Websites
ORDER BY alexa DESC;

ORDER BY 多列

SELECT * FROM Websites
ORDER BY country,alexa;

ORDER BY 多列的时候，先按照第一个column name排序，在按照第二个column name排序。