2161 In addition, the  SET TIMESTAMP  statement affects the value returned by  NOW()  but not by  SYSDATE() . This means that timestamp settings in the binary log have no effect on invocations of  SYSDATE() . Setting the timestamp to a nonzero value causes each subsequent invocation of  NOW()  to return that value. Setting the timestamp to zero cancels this effect so that  NOW()  once again returns the current date and time. See the description for  SYSDATE()  for additional information about the differences between the two functions. Adds  N  months to period  P  (in the format  YYMM  or  YYYYMM ). Returns a value in the format  YYYYMM . The period argument  P  is  not  a date value. Note Returns the number of months between periods  P1  and  P2 .  P1  and  P2  should be in the format  YYMM  or YYYYMM . Note that the period arguments  P1  and  P2  are  not  date values. Returns the quarter of the year for  date , in the range  1  to  4 . Returns the second for  time , in the range  0  to  59 . Returns the  seconds  argument, converted to hours, minutes, and seconds, as a  TIME  value. The range of the result is constrained to that of the  TIME  data type. A warning occurs if the argument corresponds to a value outside that range. mysql>  SELECT SEC_TO_TIME(2378); -> ’00:39:38’ mysql>  SELECT SEC_TO_TIME(2378) + 0; -> 3938 mysql>  SELECT SECOND(’10:05:03’); -> 3 mysql>  SELECT QUARTER(’2008-04-01’); -> 2 mysql>  SELECT PERIOD_DIFF(200802,200703); -> 11 mysql>  SELECT PERIOD_ADD(200801,2); -> 200803 +---------------------+----------+---------------------+ | SYSDATE() | SLEEP(2) | SYSDATE() | +---------------------+----------+---------------------+ | 2006-04-12 13:47:44 | 0 | 2006-04-12 13:47:46 | +---------------------+----------+---------------------+ Date and Time Functions • PERIOD_ADD( P , N ) • PERIOD_DIFF( P1 , P2 ) • QUARTER( date ) • SECOND( time ) • SEC_TO_TIME( seconds ) • STR_TO_DATE( str , format )