mysql group相關函數

Name	Description
AVG()	Return the average value of the argument
BIT_AND()	Return bitwise and
BIT_OR()	Return bitwise or
BIT_XOR()	Return bitwise xor
COUNT(DISTINCT)	Return the count of a number of different values
COUNT()	Return a count of the number of rows returned
GROUP_CONCAT()	Return a concatenated string
MAX()	Return the maximum value
MIN()	Return the minimum value
STD()	Return the population standard deviation
STDDEV_POP()	Return the population standard deviation
STDDEV_SAMP()	Return the sample standard deviation
STDDEV()	Return the population standard deviation
SUM()	Return the sum
VAR_POP()	Return the population standard variance
VAR_SAMP()	Return the sample variance
VARIANCE()	Return the population standard variance