1. 建表脚本
${x} 是0 - 61依次取值，也就是要建62张表
CREATE TABLE `short_urls_${x}` (
  `s` varchar(16) NOT NULL DEFAULT '' COMMENT '短url的key，基于md5',
  `l` varchar(512) NOT NULL DEFAULT '' COMMENT '原始url',
  `created_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '可有可无',
  PRIMARY KEY (`s`),
  KEY `created_at` (`created_at`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='短url表，后续可能按照key前缀分表';

2. 表名与key首字符对应关系
        0 => short_urls_0, 
        1 => short_urls_1, 
        2 => short_urls_2, 
        3 => short_urls_3, 
        4 => short_urls_4, 
        5 => short_urls_5, 
        6 => short_urls_6, 
        7 => short_urls_7, 
        8 => short_urls_8, 
        9 => short_urls_9, 
        A => short_urls_10, 
        B => short_urls_11, 
        C => short_urls_12, 
        D => short_urls_13, 
        E => short_urls_14, 
        F => short_urls_15, 
        G => short_urls_16, 
        H => short_urls_17, 
        I => short_urls_18, 
        J => short_urls_19, 
        K => short_urls_20, 
        L => short_urls_21, 
        M => short_urls_22, 
        N => short_urls_23, 
        O => short_urls_24, 
        P => short_urls_25, 
        Q => short_urls_26, 
        R => short_urls_27, 
        S => short_urls_28, 
        T => short_urls_29, 
        U => short_urls_30, 
        V => short_urls_31, 
        W => short_urls_32, 
        X => short_urls_33, 
        Y => short_urls_34, 
        Z => short_urls_35, 
        a => short_urls_36, 
        b => short_urls_37, 
        c => short_urls_38, 
        d => short_urls_39, 
        e => short_urls_40, 
        f => short_urls_41, 
        g => short_urls_42, 
        h => short_urls_43, 
        i => short_urls_44, 
        j => short_urls_45, 
        k => short_urls_46, 
        l => short_urls_47, 
        m => short_urls_48, 
        n => short_urls_49, 
        o => short_urls_50, 
        p => short_urls_51, 
        q => short_urls_52, 
        r => short_urls_53, 
        s => short_urls_54, 
        t => short_urls_55, 
        u => short_urls_56, 
        v => short_urls_57, 
        w => short_urls_58, 
        x => short_urls_59, 
        y => short_urls_60, 
        z => short_urls_61