关于mysql多个字段update时错误使用and连接字段的问题
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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