Function encode_structured_json 

fn encode_structured_json<S: Encoder>(
    query_ctx: &QueryContextRef,
    column: &ArrayRef,
    i: usize,
    encoder: &mut S,
    pg_field: &FieldInfo,
) -> PgWireResult<()>

Encodes one row of a structured column (Struct, or List of Struct) as a PostgreSQL json value.

Returns an error for arrow field types greptimedb cannot represent (e.g. Decimal256) instead of panicking, so the client receives a proper error response.