大查询 - 用户定义函数 - 标量子查询错误

Posted 2023-03-24

【中文标题】大查询 - 用户定义函数 - 标量子查询错误

【英文标题】：Big Query - User Defined Function - Scalar Subquery Error

【发布时间】：2020-11-25 03:11:11

【问题描述】：

我正在尝试根据下面的查询重新创建用户定义的函数，但是，当我运行它时，它反而返回了这个错误。感谢这里是否有人知道解决方法。

标量子查询产生了多个元素：

create or replace function `dataset.list_of_days`
(user_id string, start_date date, end_date date) AS 
((
with temp as (
  select user_id, day from
  unnest(generate_date_array(start_date, end_date)) day)   

select as struct row_number() over (partition by user_id order by day asc) as row_num,
       user_id, day
from temp
  ));

with temp as (
select '100110' as user_id, date('2020-01-31') as start_date,
       date('2020-02-28') as end_date )
       
select dataset.list_of_days(user_id, start_date, end_date)
from temp;

【问题讨论】：

如果我错了请纠正我，但我可能误解了用户定义函数的目的是什么

【参考方案1】：

BigQuery 的 UDF 只能返回一个标量值，看来你的 UDF 内部没有太大的输出，你可以考虑重写为

create or replace function `dataset.list_of_days`
(user_id string, start_date date, end_date date) AS 

(ARRAY(   -- NOTE: ARRAY() was added to you original query

with temp as (
  select user_id, day from
  unnest(generate_date_array(start_date, end_date)) day)   

select as struct row_number() over (partition by user_id order by day asc) as row_num,
       user_id, day
from temp
  ));

with temp as (
select '100110' as user_id, date('2020-01-31') as start_date,
       date('2020-02-28') as end_date )
       
select dataset.list_of_days(user_id, start_date, end_date)
from temp;

注意现在UDF的返回类型是ARRAY>，如果你需要它作为一个多行的表，你可以取消嵌套。