MySQL自动将字符串转换/转换为数字?

问题描述

MySQL 是否自动将字符串转换为数值?
这种转换是如何工作的?

Does MySQL automatically casting\converting the string to numeric value?
How does that conversion works?

• '1234'=1234 ?
• '1abc' = 1 ?
• 'text' = 1 ?

鉴于 units.id 是 bigint 类型，将如何解释此查询?

Given that units.id is of bigint type, how this query will be interpreted?

SELECT table.* 
FROM table 
WHERE id='text'

推荐答案

前三个问题的答案是:是、是和否.

The answers to your first three questions are: yes, yes, and no.

当字符串'text'被转换为数字时，它变成了值0.

When the string 'text' is converted to a number, it becomes the value 0.

描述类型转换的文档在这里.

The documentation that describes type conversion is here.

对于您的查询:

SELECT table.* 
FROM table 
WHERE id='text';

此规则摘录自文档:

在所有其他情况下，参数作为浮点(实数)数进行比较.

In all other cases, the arguments are compared as floating-point (real) numbers.

换句话说，这实际上相当于:

In other words, this is actually equivalent to:

WHERE id = 0.0

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