MySQL varchar唯一列varchar(255)与varchar(50) [英] Mysql varchar unique column varchar(255) vs. varchar(50)

问题描述

我将始终在表的特定列中输入20个字符.

I will always be entering things of 20 characters into a particular column in my table.

我需要此列是唯一的.

如果我将此列设置为varchar(255)而不是varchar(20)，那么SELECT查询中是否会有速度差异?

Will there be any speed difference in SELECT queries if I set this column to be a varchar(255) instead of varchar(20)?

(输入的数据始终为20个字符)

(data entered will always be 20 characters)

推荐答案

如果输入的数据总是 20个字符，那么为什么不考虑使用 char(20).使用varchar(20)将使用20个字节存储字符，并使用1个字节存储长度.因此，如果有100万条记录，则会浪费100万个字节.

if data entered will always be 20 characters than why not consider using char(20). using varchar(20) will use 20 bytes for storing character and 1 byte for storing length. so if there are 1 million records, 1 million bytes will be wasted.

就varchar(20)和varchar(255)之间的速度而言，那么我认为选择它们之一可能很难，因为它们都将使用21个字节，我看不到任何显着的性能一个人的利益或损失.

as far as speed is concerned between varchar(20) and varchar(255), then I dont think it might be very hard to pick one of them, both of them will be using 21 bytes, I dont see any significant performance benefit or loss of one over other.

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