SELECT commands
Data can be queried from a hypertable using the standard SELECT
SQL command (PostgreSQL docs), including with arbitrary WHERE
clauses, GROUP BY
and ORDER BY
commands, joins, subqueries, window functions, user-defined functions (UDFs), HAVING
clauses, and so on.
From basic queries:
-- Return the most recent 100 entries in the table 'conditions' ordered newest to oldest
SELECT * FROM conditions ORDER BY time DESC LIMIT 100;
-- Return the number of data entries written in past 12 hours
SELECT COUNT(*) FROM conditions
WHERE time > NOW() - INTERVAL '12 hours';
To more advanced SQL queries:
-- Information about each 15-min period for each location
-- over the past 3 hours, ordered by time and temperature
SELECT time_bucket('15 minutes', time) AS fifteen_min,
location, COUNT(*),
MAX(temperature) AS max_temp,
MAX(humidity) AS max_hum
FROM conditions
WHERE time > NOW() - INTERVAL '3 hours'
GROUP BY fifteen_min, location
ORDER BY fifteen_min DESC, max_temp DESC;
-- How many distinct locations with air conditioning
-- have reported data in the past day
SELECT COUNT(DISTINCT location) FROM conditions
JOIN locations
ON conditions.location = locations.location
WHERE locations.air_conditioning = True
AND time > NOW() - INTERVAL '1 day'
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