GROUP BY

Aggregate rows into groups:

SELECT
    DATE_TRUNC('month', time) AS month,
    AVG(temperature)          AS avg_temp,
    MIN(temperature)          AS min_temp,
    MAX(temperature)          AS max_temp,
    COUNT(*)                  AS observations
FROM ocean_profiles
WHERE depth < 10
GROUP BY DATE_TRUNC('month', time)
ORDER BY month

Grouping by multiple columns

SELECT
    DATE_TRUNC('year', time) AS year,
    FLOOR(latitude / 10) * 10 AS lat_band,
    AVG(temperature) AS avg_temp
FROM ocean_profiles
GROUP BY year, lat_band
ORDER BY year, lat_band

HAVING

Filter groups after aggregation (unlike WHERE, which filters rows before grouping):

SELECT
    FLOOR(latitude / 5) * 5 AS lat_bin,
    AVG(temperature)        AS avg_temp,
    COUNT(*)                AS observations
FROM ocean_profiles
GROUP BY lat_bin
HAVING COUNT(*) > 100
ORDER BY lat_bin

Common aggregate functions

Function	Description
COUNT(*)	Total rows in the group
COUNT(col)	Non-NULL values in the group
SUM(col)	Sum
AVG(col)	Mean
MIN(col)	Minimum
MAX(col)	Maximum
STDDEV(col)	Standard deviation
MEDIAN(col)	Median

See Function Reference for the full list.