Retrieval using standard aggregate functions
Using the SELECT command to return data and apply standard aggregate functions.
In Cassandra 2.2, the standard aggregate functions of min
,
max
, avg
, sum
, and
count
are built-in functions.
Procedure
-
A table cyclist_points records the race points for
cyclists.
cqlsh> CREATE TABLE cycling.cyclist_points (id UUID, firstname text, lastname text, race_title text, race_points int, PRIMARY KEY (id, race_points );
-
Calculate the standard aggregation function
sum
to find the sum of race points for a particular cyclist. The value of the aggregate will be returned.cqlsh> SELECT sum(race_points) FROM cycling.cyclist_points WHERE id=e3b19ec4-774a-4d1c-9e5a-decec1e30aac;
-
Another standard aggregate function is
count
. A table country_flag records the country of each cyclist.CREATE TABLE cycling.country_flag (country text, cyclist_name text, flag int STATIC, PRIMARY KEY (country, cyclist_name));
-
Calculate the standard aggregation function
count
to find the number of cyclists from Belgium. The value of the aggregate will be returned.cqlsh> SELECT count(cyclist_name) FROM cycling.country_flag WHERE country='Belgium';