Build Your Own DatabaseDriven Website Using PHP amp;amp; MySQL [Electronic resources] نسخه متنی

COUNT(expr)

This function returns a count of the number of times in the ungrouped
result set that expr had a non-NULL value.
If COUNT(*) is used, it will simply provide a count of
the number of rows in the group, irrespective of NULL values.

COUNT(DISTINCT expr[,expr ...])

This function returns a count of the number of different non-NULL values
(or sets of values, if multiple expressions are provided).

AVG(expr)

This function calculates the arithmetic mean (average) of the values
appearing in the rows of the group.

MIN(expr),MAX(expr)

This function returns the smallest or largest value of expr in
the rows of the group.

SUM(expr)

This function returns the sum of the values for expr in
the rows of the group.

STD(expr),STDDEV(expr)

This function returns the standard deviation of the values for expr in
the rows of the group (either of the two function names may be used).

BIT_OR(expr),BIT_AND(expr)

This function calculates the bit-wise OR and the bit-wise AND of the
values for expr in the rows of the group, respectively.