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执行语句一

update spoken set book_id = 2 and unit_id = 14 and article_id = 47409 where id = 284989;

结果为只将book_id字段值更新为0,其他字段都没有更改

mysql> select id,book_id,unit_id,article_id from spoken;

+--------+---------+---------+------------+

| id     | book_id | unit_id | article_id |

+--------+---------+---------+------------+

| 284989 |       5 |      55 |      55555 |

+--------+---------+---------+------------+

1 row in set (0.00 sec)

mysql> update spoken set book_id = 2 and unit_id = 14 and article_id = 47409 where id = 284989;

Query OK, 1 row affected (0.00 sec)

Rows matched: 1  Changed: 1  Warnings: 0

mysql> select id,book_id,unit_id,article_id from spoken;

+--------+---------+---------+------------+

| id     | book_id | unit_id | article_id |

+--------+---------+---------+------------+

| 284989 |       0 |      55 |      55555 |

+--------+---------+---------+------------+

1 row in set (0.00 sec)

 

执行语句二

update spoken set book_id = 2,unit_id = 14,article_id = 47409 where id = 284989;（正常语句）

三个字段值都变更为给定值，

mysql> select id,book_id,unit_id,article_id from spoken;

+--------+---------+---------+------------+

| id     | book_id | unit_id | article_id |

+--------+---------+---------+------------+

| 284989 |       0 |      55 |      55555 |

+--------+---------+---------+------------+

1 row in set (0.00 sec)

mysql> update spoken set book_id = 2,unit_id = 14,article_id = 47409 where id = 284989;          

Query OK, 1 row affected (0.00 sec)

Rows matched: 1  Changed: 1  Warnings: 0

mysql> select id,book_id,unit_id,article_id from spoken;

+--------+---------+---------+------------+

| id     | book_id | unit_id | article_id |

+--------+---------+---------+------------+

| 284989 |       2 |      14 |      47409 |

+--------+---------+---------+------------+

1 row in set (0.00 sec)

 

执行语句三

update spoken set book_id = 2 and unit_id = 14 and article_id = 47409 where id = 284989;

只将第一个字段变更为1

mysql> select id,book_id,unit_id,article_id from spoken;

+--------+---------+---------+------------+

| id     | book_id | unit_id | article_id |

+--------+---------+---------+------------+

| 284989 |       2 |      14 |      47409 |

+--------+---------+---------+------------+

1 row in set (0.00 sec)

mysql> update spoken set book_id = 2 and unit_id = 14 and article_id = 47409 where id = 284989;   

Query OK, 1 row affected (0.00 sec)

Rows matched: 1  Changed: 1  Warnings: 0

mysql> select id,book_id,unit_id,article_id from spoken;

+--------+---------+---------+------------+

| id     | book_id | unit_id | article_id |

+--------+---------+---------+------------+

| 284989 |       1 |      14 |      47409 |

+--------+---------+---------+------------+

1 row in set (0.00 sec)

分析，

1、正常的update语法为语句二，更新多个字段的值，多个字段之间使用逗号“，”分隔。

2、但问题语句一和问题语句三更新多个字段的值使用and ，分隔多个字段；

且语句一将book_id变更为，语句三将book_id变更为1；

一、问题语句一

update spoken set book_id = 2 and unit_id = 14 and article_id = 47409 where id = 284989;

等价于

update spoken set book_id = (2 and unit_id = 14 and article_id = 47409) where id = 284989;

等价于

update spoken set book_id = (2 and (unit_id = 14) and (article_id = 47409)) where id = 284989;

相当于将book_id的值更新为下面语句的值

select 2 and (unit_id = 14) and (article_id = 47409) from spoken where id = 284989;

该语句由三个表达式通过mysql的逻辑运算符and连接

表达式一为:  2

表达式二为：unit_id = 14 （select unit_id = 14 from spoken where id = 284989;）

表达式三为：article_id = 47409 （select article_id = 47409 from spoken where id = 284989;）

由于当时unit_id = 55,article_id=55555

表达一的值为2

表达式二值为0

表达式三的值为0

所以select 2 and (unit_id = 14) and (article_id = 47409) from spoken where id = 284989;

的值为2 and 0 and 0 即为。

即执行语句的结果等价于update spoken set book_id = 0 where id = 284989;

Mysql的逻辑运算

http://www.cnblogs.com/pzk7788/p/6891299.html

逻辑与 ( AND 或 && )

(1) 当所有操作数均为非零值、并且不为 NULL 时，所得值为 1
(2) 当一个或多个操作数为 0 时，所得值为 0 
(3) 其余情况所得值为 NULL

mysql> SELECT 1 AND -1, 1 && 0, 0 AND NULL, 1 && NULL ;
+----------+--------+------------+-----------+
| 1 AND -1  | 1 && 0  | 0 AND NULL | 1 && NULL |
+----------+--------+------------+-----------+
| 1         | 0       | 0           | NULL      |
+----------+--------+------------+-----------+

二、同理可得语句三

2 and unit_id = 14 and article_id = 47409

相当于将book_id的值更新为下面语句的值

select 2 and (unit_id = 14) and (article_id = 47409) from spoken where id = 284989;

该语句由三个表达式通过mysql的逻辑运算符and连接

表达式一为:  2

表达式二为：unit_id = 14 （select unit_id = 14 from spoken where id = 284989;）

表达式三为：article_id = 47409 （select article_id = 47409 from spoken where id = 284989;）

由于当时unit_id = 14,article_id=47409

表达一的值为2

表达式二值为1

表达式三的值为1

所以select 2 and (unit_id = 14) and (article_id = 47409) from spoken where id = 284989;

的值为2 and 1 and 1 即为1。

即执行语句的结果等价于update spoken set book_id = 1 where id = 284989;

额外的问题：

Mysql如果对mysql的数值型如int做匹配时，unit_id字段和14做匹配时

如下三个语句都匹配到结果

select id,book_id,unit_id,article_id from spoken where unit_id=14;

select id,book_id,unit_id,article_id from spoken where unit_id='14';

select id,book_id,unit_id,article_id from spoken where unit_id='14aaa';

（字符串转数值会截取第一个非数字前面的数字）

mysql>  select id,book_id,unit_id,article_id from spoken where unit_id=14;

+--------+---------+---------+------------+

| id     | book_id | unit_id | article_id |

+--------+---------+---------+------------+

| 284989 |       0 |      14 |      47409 |

+--------+---------+---------+------------+

1 row in set (0.00 sec)

mysql> select id,book_id,unit_id,article_id from spoken where unit_id='14';

+--------+---------+---------+------------+

| id     | book_id | unit_id | article_id |

+--------+---------+---------+------------+

| 284989 |       0 |      14 |      47409 |

+--------+---------+---------+------------+

1 row in set (0.00 sec)

mysql> select id,book_id,unit_id,article_id from spoken where unit_id='14aaa';

+--------+---------+---------+------------+

| id     | book_id | unit_id | article_id |

+--------+---------+---------+------------+

| 284989 |       0 |      14 |      47409 |

+--------+---------+---------+------------+

1 row in set, 1 warning (0.00 sec)

 

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