相当于R查询的sql

Question

我有两个数据集 author_data 和 paper_author

作者数据:

author_id       author_name          author_affiliation
 25         William H. Nailon                                                                    
 37         P. B. Littlewood        Cavendish Laboratory|Cambridge University
 44         A. Kuroiwa               Department of Molecular Biology 

论文作者:

paper_id     author_id      author_name      author_affiliation
  1          521630         Ayman Kaheel     Cairo Microsoft Innovation Lab
  1          972575       Mahmoud Refaat     Cairo Microsoft Innovation Lab

我在 R 中运行了以下查询

author_data[which(author_data$author_id %in% paper_author$author_id &
                  author_data$author_name %in% paper_author$author_name & 
                  author_data$author_affiliation %in% paper_author$author_affiliation), ]

也就是说，我想找出 author_data 和 paper_author 之间的匹配项，其中 author_id、author_name 和 author_affiliation 三列匹配。

我已经写了一个查询来在 sql 中得到这个结果，但我没有得到正确的结果。我试过的查询是

statement <- "select
              author_data.author_id,
              author_data.author_name,
              author_data.author_affiliation
        FROM author_data
        INNER JOIN paper_author
          ON author_data.author_id = paper_author.author_id
            AND author_data.author_name = paper_author.author_name
            AND author_data.author_affiliation = paper_author.author_affiliation"

通过这个查询，我得到的行比 author_data 中的行多，查询应该获取首先是 author_data 子集的数据。由于我对 sql 很天真，所以无法弄清楚问题出在哪里。

这个查询有什么问题？

谢谢

Answer 1

R 中的 which 和 SQL 中的 join 是有区别的。 which 将有效地对给定的数据帧进行子集化，而 join 将返回满足 join 条件的所有行。我几乎可以肯定，在您的情况下，您在 paper_author 中多次出现 author_id, author_name, author_affiliation 组合。因此，author_data 中的行乘以 paper_author 中的行。

您的查询几乎是正确的，您需要添加 distinct 或 group by 或使用 exists:

区别:

select
   distinct
   author_data.author_id,
   author_data.author_name,
   author_data.author_affiliation
from
   author_data
   INNER JOIN paper_author
          ON author_data.author_id = paper_author.author_id
            AND author_data.author_name = paper_author.author_name
            AND author_data.author_affiliation = paper_author.author_affiliation

分组依据:

select
   author_data.author_id,
   author_data.author_name,
   author_data.author_affiliation
from
   author_data
   INNER JOIN paper_author
          ON author_data.author_id = paper_author.author_id
            AND author_data.author_name = paper_author.author_name
            AND author_data.author_affiliation = paper_author.author_affiliation
group by
   author_data.author_id,
   author_data.author_name,
   author_data.author_affiliation

你也可以使用exists:

select
   author_data.author_id,
   author_data.author_name,
   author_data.author_affiliation
from
   author_data
where
   exists (select 1 from paper_author where
       author_data.author_id = paper_author.author_id
       AND author_data.author_name = paper_author.author_name
       AND author_data.author_affiliation = paper_author.author_affiliation
       )