Aggregate
functions operate on a set of data. These are usually used to perform
some action on a complete set of returned rows. For example,
SELECT
AVG(height) FROM kids
would return the average of all the values of the
height
field in the kids
table.
AVG(
expression
)
Returns the average value of the values in
expression
(e.g., SELECT
AVG(score)
FROM tests
).
BIT_AND(
expression
)
Returns the bitwise AND
aggregate of all the
values in expression
(e.g.,
SELECT
BIT_AND(flags) FROM
options
). A bit will be set in the result if and only if
the bit is set in every input field.
BIT_OR(
expression
)
Returns the bitwise OR
aggregate of all the values
in expression
(e.g.,
SELECT
BIT_OR(flags) FROM
options
). A bit is set in the result if it is set in at
least one of the input fields.
COUNT(
expression
)
Returns the number of times expression
was
not null. COUNT(*)
will return the number of rows
with some data in the entire table (e.g., SELECT
COUNT(*)
FROM
folders
).
MAX(
expression
)
Returns the largest value in expression
(e.g., SELECT
MAX
(elevation)
FROM mountains
).
MIN(
expression
)
Returns the smallest value in expression
(e.g., SELECT
MIN(level)
FROM
toxic_waste
).
STD(
expression
)/STDDEV(
expression
)
Returns the standard deviation of the values in
expression
(e.g.,
SELECT
STDDEV(points) FROM
data
).
SUM(
expression
)
Returns the sum of the values in
expression
(e.g., SELECT
SUM(calories) FROM
daily_diet
).
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