在BigQuery中加入CTE结果时如何更新表? [英] How to update table while joining on CTE results in BigQuery?

问题描述

我认为通过这个简化的示例(在PostgreSQL中可以工作)可以看到我正在尝试做什么....

I think it will be obvious to see what I'm trying to do through this simplified example (works in PostgreSQL)....

with a as
(
    select 1 as id, 123.456 as value
)
update 
    mytable 
    set value = coalesce(a1.value, a2.value) 
from 
    a as a1, 
    a as a2 
where 
    a1.id = mytable.id 
or 
    a2.id = mytable.id2

这是一个简化的示例.实际上，"a"表达式非常复杂，我需要在update表达式中多次加入该表达式.有没有办法在BigQuery的一条语句中做到这一点?

This is a simplified example. In reality the "a" expression is pretty complex and I need to join to it multiple times in the update expression. Is there a way to do this in one statement in BigQuery?

现在，我看到的唯一选择是首先在单独的查询中将"a"创建为表，然后执行更新.可以，但是这需要经常按计划运行，因此不是最佳选择.

Right now, the only option I see is to first create "a" as a table in a separate query, and then perform the update. That can work, but this is something that needs to run frequently on a schedule so it's not optimal.

推荐答案

您可以将update语句转换为下面的

You can transform you update statement into below

#standardSQL
UPDATE 
  `project.dataset.mytable` mytable 
  SET value = new_value 
FROM (
  WITH a AS
  (
    SELECT 1 AS id, 123.456 AS value
  )  
  SELECT a1.id a1_id, a2.id a2_id, 
    COALESCE(a1.value, a2.value) new_value
  FROM 
    a AS a1, 
    a AS a2 
)
WHERE 
  a1_id = mytable.id 
OR 
  a2_id = mytable.id2

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