Function arrayAgg

Aggregate values into an array/JSON-array, dispatched per-dialect.

• PostgreSQL / CockroachDB: native ARRAY_AGG([DISTINCT] expr [ORDER BY col [ASC|DESC]]).
• Snowflake: native ARRAY_AGG([DISTINCT] expr) [WITHIN GROUP (ORDER BY col [ASC|DESC])] — Snowflake's ARRAY_AGG uses the same WITHIN GROUP placement as LISTAGG, not Postgres's inline ORDER BY.
• ClickHouse: native groupArray(expr) (distinct: groupUniqArray(expr)); returns ClickHouse's native Array(T) type. No inline ORDER BY support (same limitation as stringAgg) — throws if orderBy is requested.
• MySQL (5.7.22+) / MariaDB (10.5+): no ARRAY_AGG, but both support the real JSON_ARRAYAGG(expr) function, used here as a JSON-array fallback. Neither dialect's JSON_ARRAYAGG supports DISTINCT or ORDER BY — both throw if requested.
• Oracle (12.2+) / Db2 (11.5+): no ARRAY_AGG, but both support the real SQL:2016 JSON_ARRAYAGG(expr) function, used as a JSON-array fallback here too. DISTINCT/ORDER BY throw (not supported by either engine's JSON_ARRAYAGG).
• SQLite: no ARRAY_AGG, but has the real native json_group_array(expr) aggregate, used as the fallback. DISTINCT/ORDER BY throw (not supported by SQLite's json_group_array).
• MSSQL / Redshift: no real array-aggregation concept and no reliable scalar-aggregate JSON-array equivalent (MSSQL's JSON array construction is via FOR JSON PATH on a full query shape, not an aggregate function usable inline in a SELECT list; Redshift has no JSON_ARRAYAGG). Both throw a clear "not supported" error rather than faking an unreliable workaround.