Nested aggregate functions with grouping in postgresql

You need a subquery:

select z, avg(sumval)from (select y, z, sum(x) as sumval      from t      group by y, z     ) tgroup by z

sql postgresql grouping aggregate

You could also use a Common Table Expression (CTE) for that:

WITH tmp AS (    SELECT y, z, sum(x) as sumval    FROM t    GROUP BY y, z)SELECT z, avg(sumval)FROM tmpGROUP BY z

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