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mysql varchar实际存储位数

mysql 对于 varchr 类型,若位数小于 256,会多加一个字节存储(用来保存长度),大于 255 的会多加两个字节存储,详见 mysql 文档

VARCHAR(_`M`_), VARBINARY(_`M`_)
L + 1 bytes if column values require 0 ? 255 bytes, L + 2 bytes if values may require more than 255 bytes

为什么我用 LENGTH 函数得到的字节数没有加上呢?

SELECT LENGTH('a'); -- 1,为什么不是 2?
-- 从表字段里面计算也是一样的

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LENGTH()方法是获取字符串长度,不是获取字节大小,谢谢,关注

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