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1. adddate(date,interval expr unit) unit include (microsecond,second,minute,hour,day,month,quarter,year,seconde_microsecond,minute_microsecond,minute_second,hour_microsecond,hour_second,hour_minute,day_microsecond,day_second,day_minute,day_hour,year_month)

   unit Value Expected expr Format MICROSECOND MICROSECONDS SECOND SECONDS MINUTE MINUTES HOUR HOURS DAY DAYS WEEK WEEKS MONTH MONTHS QUARTER QUARTERS YEAR YEARS SECOND_MICROSECOND 'SECONDS.MICROSECONDS' MINUTE_MICROSECOND 'MINUTES:SECONDS.MICROSECONDS' MINUTE_SECOND 'MINUTES:SECONDS' HOUR_MICROSECOND 'HOURS:MINUTES:SECONDS.MICROSECONDS' HOUR_SECOND 'HOURS:MINUTES:SECONDS' HOUR_MINUTE 'HOURS:MINUTES' DAY_MICROSECOND 'DAYS HOURS:MINUTES:SECONDS.MICROSECONDS' DAY_SECOND 'DAYS HOURS:MINUTES:SECONDS' DAY_MINUTE 'DAYS HOURS:MINUTES' DAY_HOUR 'DAYS HOURS' YEAR_MONTH 'YEARS-MONTHS'

   select adddate(now(),interval '1:30' hour_minute); select adddate(now(),interval '1' day);

2. addtime(exp1,exp2) select addtime(now(),'1 0:0'); select addtime(now(),'1 12:43');

3. curdate(),now(),curtime() select curdate() ,date(now()),curtime(),time(now());

   curdate()==current_date(),current_date curtime()==current_time(),current_time now()==current_timestamp(),current_timestamp

4. datediff(exp1,exp2) return exp1 - exp2
   select datediff('2017/1/1','2018/1/1'); //-365

   select datediff(now(),'2017/1/1'),datediff('2018/1/1',now());

5. dayofweek(),dayofyear() select dayofweek(now()),dayofyear(now()); select date(concat(year(now()),'/1/1'));

6. year(),month(),day(),hour(),minute(),second() select year(now()),month(now()),day(now());