bigquery udf 中的 WITH RECURSIVE

Question

I try to write bigquery udf with recursive cte as following code:

create or replace function accounting.monthly_sum(arr array<struct<aq numeric,ap numeric,m int64>>) returns numeric 
as (
    (
    WITH RECURSIVE 
    rec AS (
      SELECT arr[0].aq, arr[0].m,least(arr[0].aq,arr[0].ap) ar 
      UNION ALL
      SELECT series.aq,series.m, least(series.aq + rec.ar, series.ap) 
      FROM UNNEST(arr) series 
      JOIN rec ON series.m = rec.m + 1
    )
    SELECT ar
    from rec
    order by m desc
    limit 1
    )
    );

This returns an error:

SQL Error [100032] [HY000]: [Simba]BigQueryJDBCDriver Error executing query job. Message: WITH RECURSIVE is only allowed at the top level of the SELECT, CREATE TABLE AS SELECT, CREATE VIEW, INSERT, EXPORT DATA statements.

I cannot find what is the problem.

Answer 1

It seems there are some limitations using RECURSIVE CTEs :

WITH RECURSIVE is not allowed in functions.

WITH RECURSIVE is not allowed in materialized views.

• https://cloud.google.com/bigquery/docs/reference/standard-sql/query-syntax#cte_rules