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bitとかbyteとかメモる

65535なんかの数字にピンとこないと、プログラマとして「あっ...察し」って思われそうなのでまとめる。

bit, Byte

  • 1Byte = 8bit = 0~255
  • 2Byte = 16bit = 0~65535
  • 3Byte = 16bit = 0~16777215

KB, MBとの換算はこれを参考に

1文字は何バイトか?

参考によると

  • 半角文字:1バイト
  • 全角文字:2バイトとか3バイトとか4バイトとか

MySQLとbyte

varchar型

  • charは固定長
  • varcharは可変長

text型

  • 64kByte = 65535Byte制限
  • すなわち半角文字で65535byte=65535文字まで収納可能
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