修改c字段=a字段+b字段用，拼接
update tab set c=IFNULL(concat(a,',',b),a);
修改字段+1或者-1
update tab set praise_num = praise_num + 1 where id = #{id,jdbcType=INTEGER}
update tab set praise_num = praise_num - 1 where id = #{id,jdbcType=INTEGER}
模糊查询
like CONCAT(#{word,jdbcType=VARCHAR},'%')
like CONCAT('%>',CONCAT(#{deptId},'>%' )）
根据当前时间判断一个活动的状态：1已结束，2进行中，3未开始
CASE WHEN end_time < #{nowTime,jdbcType=TIMESTAMP} THEN 1
WHEN start_time <= #{nowTime,jdbcType=TIMESTAMP}
AND end_time >= #{nowTime,jdbcType=TIMESTAMP} THEN 2
WHEN.start_time >= #{nowTime,jdbcType=TIMESTAMP} THEN 3
END as status,
一对多的查询，字段用逗号拼接展示
GROUP_CONCAT(t2.tag) AS activityTag
GROUP BY t1.id
时间
date_format(a.begin_date, '%Y-%m-%d')
WHERE date(click_date) = curdate()
