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GROUP BY Clause

The GROUP BY clause specifies which grouping columns should be used to perform any aggregations in the SELECT clause. If the GROUP BY clause is specified, the query is always an aggregate query, even if no aggregations are present in the SELECT clause.

When a GROUP BY clause is specified, all tuples that have matching data in the grouping columns (i.e., all tuples that belong to the same group) will be combined. The values of the grouping columns themselves are unchanged, and any other columns can be combined using an aggregate function (such as count, sum, avg, etc).

GROUP BY ALL

Use GROUP BY ALL to GROUP BY all columns in the SELECT statement that are not wrapped in aggregate functions. This simplifies the syntax by allowing the columns list to be maintained in a single location, and prevents bugs by keeping the SELECT granularity aligned to the GROUP BY granularity (Ex: Prevents any duplication). See examples below and additional examples in the Friendlier SQL with DuckDB blog post.

Multiple Dimensions

Normally, the GROUP BY clause groups along a single dimension. Using the GROUPING SETS, CUBE or ROLLUP clauses it is possible to group along multiple dimensions. See the GROUPING SETS page for more information.

Examples

-- count the number of entries in the "addresses" table that belong to each different city
SELECT city, count(*)
FROM addresses
GROUP BY city;
-- compute the average income per city per street_name
SELECT city, street_name, avg(income)
FROM addresses
GROUP BY city, street_name;

GROUP BY ALL Examples

-- Group by city and street_name to remove any duplicate values
SELECT city, street_name
FROM addresses
GROUP BY ALL;
-- GROUP BY city, street_name
-- compute the average income per city per street_name
-- Since income is wrapped in an aggregate function, do not include it in the GROUP BY
SELECT city, street_name, avg(income)
FROM addresses
GROUP BY ALL;
-- GROUP BY city, street_name

Syntax

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Last modified: 2024-03-02