如何在select子句中使用from SQL語句加入Postgresql子查詢？

Question

我試圖寫的PostgreSQL以下查詢：

select name, author_id, count(1), 
    (select count(1) 
    from names as n2 
    where n2.id = n1.id 
     and t2.author_id = t1.author_id 
    )    
from names as n1 
group by name, author_id 

這當然會影響Microsoft SQL Server的工作，但它不是在所有的postegresql。我讀它的文檔了一下，看來我可以把它改寫爲：

select name, author_id, count(1), total      
from names as n1, (select count(1) as total 
    from names as n2 
    where n2.id = n1.id 
     and n2.author_id = t1.author_id 
    ) as total 
group by name, author_id 

但返回上postegresql以下錯誤：「在FROM不能引用的同一查詢級別的其他關係的子查詢」。所以我卡住了。有誰知道我能做到嗎？

感謝

Answer 1

我不知道我理解你的意圖完美，但也許你想要的東西下面將接近：

select n1.name, n1.author_id, count_1, total_count 
    from (select id, name, author_id, count(1) as count_1 
      from names 
      group by id, name, author_id) n1 
inner join (select id, author_id, count(1) as total_count 
       from names 
       group by id, author_id) n2 
    on (n2.id = n1.id and n2.author_id = n1.author_id) 

不幸的是這增加了通過分組第一子查詢的要求ID以及名稱和author_id，我不認爲這是想要的。我不知道如何解決這個問題，但是，因爲您需要將id加入第二個子查詢中。也許別人會想出更好的解決方案。

分享和享受。

Answer 2

我只是回答這裏有我需要根據鮑勃·賈維斯答案最終SQL的格式化版本，張貼在上面我的評論：

select n1.name, n1.author_id, cast(count_1 as numeric)/total_count 
    from (select id, name, author_id, count(1) as count_1 
      from names 
      group by id, name, author_id) n1 
inner join (select author_id, count(1) as total_count 
       from names 
       group by author_id) n2 
    on (n2.author_id = n1.author_id)