实验测试了一下 mysql 的 varchar 的最大有效长度. - V2EX
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jin7
V2EX    MySQL

实验测试了一下 mysql 的 varchar 的最大有效长度.

  •  
  •   jin7 2017-09-21 09:44:07 +08:00 6547 次点击
    这是一个创建于 2966 天前的主题,其中的信息可能已经有所发展或是发生改变。

    latin1 字符集, 65532

    utf8 字符集, 21844

    utf8mb4 字符集, 16128

    也就是说如果设定为 utf8mb4 字符集, varchar 最多能存 16128 个字符, 不论是中文还是英文.

    (65535-1-2)/1=65532

    (65535-1-2)/3=21844

    (65535-1-2)/4=16383 !=16128, 不满足这个"公式"

    官方文档: https://dev.mysql.com/doc/refman/5.7/en/char.html

    The effective maximum length of a VARCHAR is subject to the maximum row size (65,535 bytes, which is shared among all columns) and the character set used.

    10 条回复    2017-10-01 10:13:34 +08:00
    jin7
        1
    jin7  
    OP
       2017-09-21 09:46:43 +08:00
    对了, mysql 版本是 5.7.17, 存储引擎是 innodb
    jin7
        2
    jin7  
    OP
       2017-09-21 09:59:27 +08:00
    soli
        3
    soli  
       2017-09-21 10:31:47 +08:00
    有用。谢谢。
    iwishing
        4
    iwishing  
       2017-09-21 17:16:27 +08:00
    16383-16128=255
    你试试看只有一个 colume,能有多长?
    iwishing
        5
    iwishing  
       2017-09-22 12:40:08 +08:00   1
    http://img.vim-cn.com/40/aefbf9e17f48daf8a6c758a1202f4de5a67342.png

    which is shared among all columns, 所有列都共享这个长度
    jin7
        6
    jin7  
    OP
       2017-09-23 13:50:54 +08:00
    我回去试试哈
    jin7
        7
    jin7  
    OP
       2017-09-27 00:46:47 +08:00
    @iwishing 确实是这样哈.
    jin7
        8
    jin7  
    OP
       2017-09-27 00:47:56 +08:00
    @iwishing 65,535 bytes, which is shared among all columns
    之前是我没看明白这句话.
    jin7
        9
    jin7  
    OP
       2017-09-27 00:48:10 +08:00
    @iwishing 多谢
    mysql
        10
    mysql  
       2017-10-01 10:13:34 +08:00
    感谢分享
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