bigquery中如何进行子查询？

Question

我正在尝试使用 bigquery 上的 reddit 数据，并且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，我必须使用子查询来自连接同一个表，特别是我想将 id 和parent_id 连接在一起，但我需要先修改 id 才能连接。这是我尝试执行查询的方式：

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

我不知道如何解决这个问题。加入这个并让这个查询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，我刚刚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

添加以解决您评论中的其他信息：

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