########### 日期函数 ###########
select now(); -- 当时 yyyy-mm-dd hh:mm:ss
select curdate(); -- 当天 yyyy-mm-dd
select (curdate() - interval (weekday(curdate()) + 1) day); -- 本周第一天
select (curdate() - interval (day(curdate()) - 1) day); -- 本月第一天
select (curdate() - interval (dayofyear(curdate()) - 1) day); -- 本年第一天
select (now() + interval 1 month); -- 下个月今天
select last_day(curdate()); -- 本月最后一天
select last_day(curdate()) + interval 1 day; -- 下月第一天
select date_format('2014-07-08 23:59:59','%y-%m-%d %h:%i:%s') -- str to date
-- 查找今天的发帖
1. createtime >= date_format(now(),'%y-%m-%d') and createtime 2. date_format(createtime,'%y-%m-%d') = left(now(),10)
3. date_format(createtime,'%y-%m-%d') = date_format(now(),'%y-%m-%d')
4. createtime like concat(date_format(now(), '%y-%m-%d'), '%')
5. createtime >= curdate() -- and createtime
unix_timestamp(substr(from_unixtime(r.repayment_time)from 1 for 10)) unix_timestamp(substr(now()from 1 for 10))
==>
r.repayment_time and r.repayment_time >= unix_timestamp(curdate() + interval 1 day)
########### 其他函数 ###########
truncate(x ,d )
round(x ,d )
select 12000/4578, truncate(12000/4578, 10), truncate(12000/4578, 8), round(12000/4578, 8)
if(expr1,expr2,expr3)   -->  case when expr1 then expr2 else expr3 end
ifnull(expr1,expr2)     -->  case when expr1 is not null then expr1 else expr2 end
concat(str1 ,str2 ,...) -->  concat('%', ? '%')
select concat_ws('|', '1','2','3')