CREATE TABLE IF NOT EXISTS `sequences_unused`
(
    `key`         VARCHAR(64) NOT NULL COMMENT '序号英文名称',
    `type`        VARCHAR(64) NOT NULL COMMENT '序号类型',
    `seq`         BIGINT(20)  NOT NULL COMMENT '闲置的的序号',
    `create_time` DATETIME    NOT NULL COMMENT '设为闲置序号的时间',
    PRIMARY KEY (`key`, `type`, `seq`)
) COMMENT '闲置序号表';