SQL where子句

WHERE 子句

WHERE 子句用于提取那些满足指定条件的记录。

SQL WHERE 语法

SELECT column_name,column_name
FROM table_name
WHERE column_name operator value;

实例

实例数据

+----+--------------+---------------------------+-------+---------+
| id | name         | url                       | alexa | country |
+----+--------------+---------------------------+-------+---------+
| 1  | Google       | https://www.google.cm/    | 1     | USA     |
| 2  | 淘宝          | https://www.taobao.com/   | 13    | CN      |
| 3  | Facebook     | https://www.facebook.com/ | 3     | USA     |
| 4  | 百度     | https://www.baidu.com/ | 4     | CN     |
+----+--------------+---------------------------+-------+---------+

选取国家为 "CN" 的所有网站：

sql > SELECT * FROM website WHERE country='CN';

+----+--------------+---------------------------+-------+---------+
| id | name         | url                       | alexa | country |
+----+--------------+---------------------------+-------+---------+
| 2  | 淘宝          | https://www.taobao.com/   | 13    | CN      |
| 4  | 百度     | https://www.baidu.com/ | 4     | CN     |
+----+--------------+---------------------------+-------+---------+

数据类条件查询

sql > SELECT * FROM website WHERE id=4;

+----+--------------+---------------------------+-------+---------+
| id | name         | url                       | alexa | country |
+----+--------------+---------------------------+-------+---------+
| 4  | 百度     | https://www.baidu.com/ | 4     | CN     |
+----+--------------+---------------------------+-------+---------+

where子句中的条件运算符

运算符	描述
=	等于
<>	不等于。注释：在 SQL 的一些版本中，该操作符可被写成 !=
>	大于
<	小于
>=	大于等于
<=	小于等于
BETWEEN	范围查询 id between 1 and 4, id 在 [1,4] 区间的值
LIKE	like关键词查询 比如"like '%百度%'"
IN	指定针对某个列的多个可能值