GROUP BY keyword

Groups aggregation calculations by one or several keys. In QuestDB, this clause is optional.

Syntax

note

QuestDB groups aggregation results implicitly and does not require the GROUP BY keyword. It is only supported for convenience. Using the GROUP BY clause explicitly will return the same results as if the clause was omitted.

Examples

The below queries perform aggregations on a single key. Using GROUP BY explicitly or implicitly yields the same results:

Single key aggregation, explicit GROUP BY

SELECT sensorId, avg(temp)
FROM readings
GROUP BY sensorId;

Single key aggregation, implicit GROUP BY

SELECT sensorId, avg(temp)
FROM readings;

The below queries perform aggregations on multiple keys. Using GROUP BY explicitly or implicitly yields the same results:

Multiple key aggregation, explicit GROUP BY

SELECT sensorId, sensorType, avg(temp)
FROM readings
GROUP BY sensorId,sensorType;

Multiple key aggregation, implicit GROUP BY

SELECT sensorId, sensorType, avg(temp)
FROM readings;

When used explicitly, the list of keys in the GROUP BY clause must match the list of keys in the SELECT clause, otherwise an error will be returned:

Error - Column b is missing in the GROUP BY clause

SELECT a, b, avg(temp)
FROM tab
GROUP BY a;

Error - Column b is missing in the SELECT clause

SELECT a, avg(temp)
FROM tab
GROUP BY a, b;

Success - Columns match

SELECT a, b, avg(temp)
FROM tab
GROUP BY a, b;