Aggregations

is_aggregate_function: COUNT SUM AVG MIN MAX STRING_AGG ARRAY_AGG JSON_AGG JSONB_AGG JSON_OBJECT_AGG JSONB_OBJECT_AGG JSON_ARRAYAGG JSON_OBJECTAGG (crates/executor/src/catalog_fn.rs).

SELECT count(*), count(email), count(DISTINCT city) FROM users;
SELECT sum(total), avg(total), min(total), max(total) FROM orders;
SELECT string_agg(name, ', ' ORDER BY name), array_agg(id ORDER BY id) FROM users;
SELECT json_agg(payload), jsonb_agg(payload), json_object_agg(name, id) FROM users;
SELECT user_id, count(*) FROM orders GROUP BY user_id HAVING count(*) > 1;
SELECT a, b, count(*) FROM t GROUP BY GROUPING SETS ((a,b),(a),());
SELECT count(*) FILTER (WHERE total > 100) FROM orders;

Behavior (query/aggregate.rs, join/aggregate.rs)#

• COUNT(*) counts rows; COUNT(expr) skips NULL; COUNT(DISTINCT) dedups by to_sql_text (unifies 1/1.0).
• SUM/AVG: int (Int8), exact Numeric, f64 paths; empty → NULL; AVG(int) → normalized Numeric (PG typing).
• MIN/MAX via value_cmp, NULL skipped, empty → NULL.
• JSON_AGG keeps per-row values incl. SQL NULL→JSON null; JSON_OBJECT_AGG skips NULL keys.
• Modifiers: DISTINCT (fully distinct-aware for COUNT), FILTER (WHERE …), agg(x ORDER BY … [NULLS FIRST|LAST]).
• Bare SELECT COUNT(*) without WHERE answered by key count.

General engine trigger: string_agg/array_agg/json_*agg, non-column GROUP BY, multi-sets, or GROUP BY+ORDER BY.