SQL UPDATE语句:修改数据

 
SQL UPDATE 语句用于修改数据表中现有的记录(数据行)。UPDATE 通常和 WHERE 子句一起使用,用以筛选满足条件的记录;如果不使用 WHERE 子句,那么表中所有的记录都将被修改,这往往不是我们期望的。

语法

带有 WHERE 子句的 UPDATE 命令的基本语法如下:

UPDATE table_name
SET column1 = value1, column2 = value2...., columnN = valueN
WHERE [condition];

您可以使用 AND 或者 OR 运算符组合多个条件。

示例

现在有一个包含如下记录的 web 表:
+----+----------------+----------------------------+-----+-------+---------+---------+
| id | name           | url                        | age | alexa | uv      | country |
+----+----------------+----------------------------+-----+-------+---------+---------+
|  1 | 百度           | https://www.baidu.com/     |  21 |     4 |  5010.5 | CN      |
|  2 | 淘宝           | https://www.taobao.com/    |  17 |     8 | 3996.75 | CN      |
|  3 | C语言中文网    | http://c.biancheng.net/    |  12 |  7923 |   11.62 | CN      |
|  4 | Google         | https://www.google.com/    |  23 |     1 |   36474 | US      |
|  5 | GitHub         | https://github.com/        |  13 |    95 |   216.3 | US      |
|  6 | Stack Overflow | https://stackoverflow.com/ |  16 |    48 |   592.2 | US      |
|  7 | Yandex         | http://www.yandex.ru/      |  11 |    53 |  591.82 | RU      |
|  8 | VK             | https://vk.com/            |  23 |    23 |    1206 | RU      |
+----+----------------+----------------------------+-----+-------+---------+---------+
以下 SQL 语句将更新表中 id 为 6 的网站的名字(name):
UPDATE website
SET name = 'stack-overflow'
WHERE id = 6;
执行完该语句,website 表的记录如下:
+----+----------------+----------------------------+-----+-------+---------+---------+
| id | name           | url                        | age | alexa | uv      | country |
+----+----------------+----------------------------+-----+-------+---------+---------+
|  1 | 百度           | https://www.baidu.com/     |  21 |     4 |  5010.5 | CN      |
|  2 | 淘宝           | https://www.taobao.com/    |  17 |     8 | 3996.75 | CN      |
|  3 | C语言中文网    | http://c.biancheng.net/    |  12 |  7923 |   11.62 | CN      |
|  4 | Google         | https://www.google.com/    |  23 |     1 |   36474 | US      |
|  5 | GitHub         | https://github.com/        |  13 |    95 |   216.3 | US      |
|  6 | stack-overflow | https://stackoverflow.com/ |  16 |    48 |   592.2 | US      |
|  7 | Yandex         | http://www.yandex.ru/      |  11 |    53 |  591.82 | RU      |
|  8 | VK             | https://vk.com/            |  23 |    23 |    1206 | RU      |
+----+----------------+----------------------------+-----+-------+---------+---------+

如果您要修改表中所有记录的 age 和 country 值,则只需要 UPTATE 命令,不需要使用 WHERE 子句,请看下面的代码:
UPDATE website
SET age = 20, country = 'CN';
执行完该语句,CUSTOMERS 表的记录如下:
+----+----------------+----------------------------+-----+-------+---------+---------+
| id | name           | url                        | age | alexa | uv      | country |
+----+----------------+----------------------------+-----+-------+---------+---------+
|  1 | 百度           | https://www.baidu.com/     |  20 |     4 |  5010.5 | CN      |
|  2 | 淘宝           | https://www.taobao.com/    |  20 |     8 | 3996.75 | CN      |
|  3 | C语言中文网    | http://c.biancheng.net/    |  20 |  7923 |   11.62 | CN      |
|  4 | Google         | https://www.google.com/    |  20 |     1 |   36474 | CN      |
|  5 | GitHub         | https://github.com/        |  20 |    95 |   216.3 | CN      |
|  6 | Stack Overflow | https://stackoverflow.com/ |  20 |    48 |   592.2 | CN      |
|  7 | Yandex         | http://www.yandex.ru/      |  20 |    53 |  591.82 | CN      |
|  8 | VK             | https://vk.com/            |  20 |    23 |    1206 | CN      |
+----+----------------+----------------------------+-----+-------+---------+---------+