enum ('0','1','2','3') -> int type causes data increment '0' -> 1 ('x' -> x+1)

    create table x (y enum ('0','1','2','3') );

    ✓

    insert into x values ('1'),('0'),('2'),('3')

    ✓

    select * from x

    | y  |

    | :- |

    | 1  |

    | 0  |

    | 2  |

    | 3  |

    alter table x modify y tinyint unsigned;

    ✓

    select * from x;

    |  y |

    | -: |

    |  2 |

    |  1 |

    |  3 |

    |  4 |