如何在 bigquery 中进行子查询？

Question

我正在尝试使用 bigquery 上的 reddit 数据，我希望在一行中看到评论和回复。我看到 bigquery 支持子查询，但我无法构建查询。由于数据的结构，我必须使用子查询自行加入相同的 table，特别是我想将 id 和 parent_id 加入在一起，但我需要在加入之前修改 id。以下是我尝试查询的方式：

SELECT 
  p.subreddit, 
  p.body AS first_body,
  p.score AS first_score,
  CONCAT('t1_',p.id) AS first_id ,
  c.last_body,
  c.last_score,
  c.last_id 
FROM 
[fh-bigquery:reddit_comments.2016_01] p,
(
  SELECT 
    body AS last_body,
    score AS last_score,
    CONCAT('t1_',id) AS last_id,
    parent_id,
    author,
    body 
  FROM  [fh-bigquery:reddit_comments.2016_01] 
  WHERE body != '[deleted]' 
  AND author != '[deleted]' 
  AND score > 1
)  c
WHERE  p.first_id = c.parent_id  
AND p.score > 1 
AND  p.author != '[deleted]' 
AND p.body != '[deleted]';

我得到的错误是：

Field 'c.parent_id' not found in table 'fh-bigquery:reddit_comments.2016_01'; did you mean 'parent_id'?

您可以在此处运行查询： https://bigquery.cloud.google.com/table/fh-bigquery:reddit_comments.2016_01

我不确定如何解决这个问题。加入此查询并将此查询发送至运行的正确方法是什么？

Answer 1

你可能想做如下的事情（只是猜测）：

SELECT 
  p.subreddit, 
  p.body AS first_body,
  p.score AS first_score,
  CONCAT('t1_',p.id) AS first_id ,
  c.last_body,
  c.last_score,
  c.last_id 
FROM 
[fh-bigquery:reddit_comments.2016_01] p
JOIN (
  SELECT 
    body AS last_body,
    score AS last_score,
    CONCAT('t1_',id) AS last_id,
    parent_id,
    author,
    body 
  FROM  [fh-bigquery:reddit_comments.2016_01] 
  WHERE body != '[deleted]' 
  AND author != '[deleted]' 
  AND score > 1
)  c
ON  p.link_id = c.parent_id  
WHERE p.score > 1 
AND  p.author != '[deleted]' 
AND p.body != '[deleted]'
LIMIT 100

查看有关 JOIN 的更多信息

请注意，我只是将您的查询转换为正确使用 JOIN，但查询逻辑仍需要您根据需要进行完善

Added to address additional info in your comment:

SELECT 
  subreddit, 
  first_body,
  first_score,
  first_id ,
  last_body,
  last_score,
  last_id 
FROM (
  SELECT 
    subreddit, 
    body AS first_body,
    score AS first_score,
    CONCAT('t1_',id) AS first_id 
  FROM [fh-bigquery:reddit_comments.2016_01]
  WHERE score > 1 
  AND author != '[deleted]' 
  AND body != '[deleted]'
) p
JOIN (
  SELECT 
    body AS last_body,
    score AS last_score,
    CONCAT('t1_',id) AS last_id,
    parent_id,
    author,
    body 
  FROM  [fh-bigquery:reddit_comments.2016_01] 
  WHERE body != '[deleted]' 
  AND author != '[deleted]' 
  AND score > 1
)  c
ON  p.first_id = c.parent_id  
LIMIT 100

Answer 2

在 BigQuery 的 SQL 方言中，逗号表示 UNION ALL 而不是 JOIN。您需要使用 JOIN 关键字显式编写 JOIN。

我还建议将连接的两端都推入子查询，以确保在执行连接之前应用所有过滤器。（到目前为止，连接是查询中成本最高的部分，因此首先应用过滤器将确保您的查询尽可能快地运行。）

如何在 bigquery 中进行子查询？

how to do subqueries in bigquery?

sql

subquery

google-bigquery

reddit

bigdata