mysql查询显示错误结果 [英] mysql query showing wrong result

问题描述

我的数据库表是这样的

+======+===========+============+
|  ID  | user Name |user surname|
+======+===========+============+
| 100  |  name     |  surname   |
| 101  |  name     |  surname   |
| 102  |  name     |  surname   |
+===============================+

当我运行此查询时，应该不显示任何行，因为不存在具有101foo2值的行:

When i run this query which should show me no rows because there is no row with 101foo2 value :

SELECT * FROM tableName WHERE ID ='101foo2'

SELECT * FROM tableName WHERE ID = '101foo2'

我得到的结果具有相同的ID，但没有foo2字

I am getting a result with same ID without the foo2 word

+======+===========+============+
|  ID  | user Name |user surname|
+======+===========+============+
| 101  |  name     |  surname   |
+===============================+

如果我的查询是ID = '101foo2'

推荐答案

您正在混合类型. ID是整数(或数字).您正在将其与字符串进行比较.因此，MySQL需要确定用于比较的类型.使用什么类型?好吧，一串?不，一个数字.字符串将使用前导数字转换为数字.因此，它变为101并匹配.

You are mixing types. ID is an integer (or number). You are comparing it to a string. So, MySQL needs to decide what type to use for the comparison. What types gets used? Well, a string? No. A number. The string is converted to a number, using the leading digits. So, it becomes 101 and matches.

您实际上应该只将数字与数字进行比较，将字符串与字符串进行比较.您可以尝试将代码编写为:

You should really only compare numbers to numbers, and strings to strings. You could try to write the code as:

SELECT * FROM tableName WHERE ID = 101foo2

但是，您会得到一个错误.另一种可能性是强制转换为字符串:

However, you would get an error. Another possibility is to force the conversion to a string:

SELECT * FROM tableName WHERE CAST(ID as CHAR) = '101foo2'

这篇关于mysql查询显示错误结果的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！