Mysql 查询返回"；例如；尽管没有通配符，结果如何？

我真的很困惑。正在运行以下查询：

SELECT * FROM `articles` WHERE `form` = 'Depotplåster' AND `size` = 5

返回也以“5”开头的行，尽管我既没有使用类似于的

运算符，也没有使用
%
通配符运算符。为什么

size
字段的类型为
VARCHAR

SELECT * FROM `articles` WHERE `form` = 'Depotplåster' AND `size` = '5'
-- this will compare the string 'size' with the string '5'


SELECT * FROM `articles` WHERE `form` = 'Depotplåster' AND `size` = 5
-- this will convert string 'size' to integer and then compare with the integer 5


字符串到整数的转换查找字符串开头的整数，并取最大整数，直到第一个非数字字符

select '5s4'=5, 's5'=5, '5'=5 -- =>1,0,1

您应该引用5，因为MySQL将表中的字符串转换为不带引号的int。
这是因为您使用的是数值和varchar数据之间的比较。MySQL将隐式地将您的列转换为
double
，结果是
5
。请参见以下简单的测试数据：

mysql> select * from test;
+-----------------+
| name            |
+-----------------+
| 5               |
| 5 and some crap |
+-----------------+
2 rows in set (0.00 sec)
将导致：

+----+-----+----------+
| 5d | 5sd | areEqual |
+----+-----+----------+
|  5 |   5 |        1 |
+----+-----+----------+
1 row in set (0.00 sec)
+----+-----+----------+
|5d | 5sd |相等|
+----+-----+----------+
|  5 |   5 |        1 |
+----+-----+----------+
一行一组（0.00秒）
-如您所见，非重要部分刚刚被截断（如上面的警告消息中所述）
您是否尝试将5括在单引号内？我猜，因为您没有将
5
作为字符串（
'5'
）引用，所以您正在强制将列转换为整数，显然，
5x1 plåster
，当转换成整数时，是5。我有点惊讶mysql不会就额外的文本向您发出警告。谢谢。所以这只是我这边的一个简单错误。希望其他人能像我一样来这里学习：）
mysql> select * from test where name = '5';
+------+
| name |
+------+
| 5    |
+------+
1 row in set (0.00 sec)
mysql> select * from test where name = 5;
+-----------------+
| name            |
+-----------------+
| 5               |
| 5 and some crap |
+-----------------+
2 rows in set, 1 warning (0.05 sec)
+---------+------+-----------------------------------------------------+
| Level   | Code | Message                                             |
+---------+------+-----------------------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: '5 and some crap' |
+---------+------+-----------------------------------------------------+
1 row in set (0.00 sec)
SELECT 
  CAST('5' AS DECIMAL) AS 5d, 
  CAST('5 and some crap' AS DECIMAL) AS 5sd, 
  CAST('5' AS DECIMAL) = CAST('5 and some crap' AS DECIMAL) AS areEqual;

+----+-----+----------+
| 5d | 5sd | areEqual |
+----+-----+----------+
|  5 |   5 |        1 |
+----+-----+----------+
1 row in set (0.00 sec)