Data aggregation

SELECT
    series_id,
    season_id,
    COUNT(*) AS cnt  -- Aggregation function COUNT returns the number of rows
                     -- output by the query.
                     -- Asterisk (*) specifies that COUNT
                     -- counts the total number of rows in the table.
                     -- COUNT(*) returns the number of rows in
                     -- the specified table, preserving the duplicate rows.
                     -- It counts each row separately.
                     -- The result includes rows that contain null values.
FROM episodes

GROUP BY
    series_id,       -- The query result will follow the listed order of columns.
    season_id        -- Multiple columns are separated by a comma.
                     -- Other columns can be listed after a SELECT only if
                     -- they are passed to an aggregate function.
ORDER BY
    series_id,
    season_id
;

COMMIT;