如果 BigQuery 中没有要显示的数据，如何 return 空值

Question

我的问题是，当 BigQuery 中“没有要显示的数据”时，我想获取空值。

像这样：

但是只有聚合函数才有效。如何修改以下查询以便 returns 空值？

我的查询：

 select oid, date, coalesce(sum(quantity_sold),0) as quantity_sold
 from table
 where oid = 'xxx' and (date >= 'xxx' and date <= 'xxx')
 group by 1,2

Answer 1

我发现这与相似，但它创建了一个包含“未找到结果”消息的列，并将空值分配给其他列。您可以应用此查询并删除消息并仅保留空值，您的查询将如下所示：

with sample_data as (
select 123 as oid, '2022-01-01' as date, 23 as quantity_sold 
union all select 111 as oid, '2022-01-02' as date, 24 as quantity_sold 
),

actual_query as (
    select oid,date,coalesce(sum(quantity_sold),0) as quantity_sold 
    from sample_data  
    where oid = 534 and (date >= '2021-03-23' and date <= '2021-04-23')
    group by 1,2
)

-- query below is the modified query from the linked SO question above

select actual_query.* 
from actual_query
union all
select actual_query.*  -- all the `actual_query` columns will be `NULL`
from (select 1) left join
     actual_query
     on 1 = 0  -- always false
where not exists (select 1 from actual_query);

示例输出：

注意：我为示例数据创建了运行dom 值，当我运行您的查询时，这些值可以模仿消息“没有要显示的数据”。

如果 BigQuery 中没有要显示的数据，如何 return 空值

How to return null values if there is no data to display in BigQuery

google-bigquery