具有多个参数的 GROUP BY 和 COUNT

Question

我有一个简单的配置： 2 个表以 many-to-many 关系链接，所以它给了我 3 个表。

Table作者：

idAuthor INT
name VARCHAR

Table 发表：

idPublication INT,
title VARCHAR,
date YEAR,
type VARCHAR,
conference VARCHAR,
journal VARCHAR

Table author_has_publication:

Author_idAuthor,
Publication_idPublication

我正在尝试获取在 SIGMOD 会议和 PVLDB 会议上发表至少 2 篇论文的所有作者姓名。现在我实现了这一点，但我仍然有双重结果。我的查询：

SELECT author.name, publication.journal, COUNT(*)
FROM author
INNER JOIN author_has_publication
    ON author.idAuthor = author_has_publication.Author_idAuthor
INNER JOIN publication
    ON author_has_publication.Publication_idPublication = publication.idPublication
GROUP BY publication.journal, author.name
HAVING COUNT(*) >= 2
   AND (publication.journal = 'PVLDB' OR  publication.journal = 'SIGMOD');

returns

+-------+---------+----------+
| name  | journal | COUNT(*) |
+-------+---------+----------+
| Renee | PVLDB   |        2 |
| Renee | SIGMOD  |        2 |
+-------+---------+----------+

如您所见，结果是正确的，但加倍了，因为我只想要 1 倍的名称。

其他问题，如何只修改一个会议的number参数，比如获取所有发布至少3个SIGMOD和至少1个PVLDB的作者？

Answer 1

如果您不关心 journal ，请不要 select 它，它会拆分您的结果。此外，普通过滤器需要放在 WHERE 子句中，而不是 HAVING 子句中：

SELECT author.name, COUNT(*)
  FROM author
 INNER JOIN author_has_publication
    ON author.idAuthor = author_has_publication.Author_idAuthor
 INNER JOIN publication
    ON author_has_publication.Publication_idPublication =
       publication.idPublication
WHERE  publication.journal IN('PVLDB','SIGMOD')       
 GROUP BY author.name
HAVING COUNT(CASE WHEN publication.journal = 'SIGMOD' THEN 1 END) >= 2
   AND COUNT(CASE WHEN publication.journal = 'PVLDB' THEN 1 END) >= 2;

对于第二个问题，使用这个 HAVING() 子句：

HAVING COUNT(CASE WHEN publication.journal = 'SIGMOD' THEN 1 END) >= 3
   AND COUNT(CASE WHEN publication.journal = 'PVLDB' THEN 1 END) >= 1;

具有多个参数的 GROUP BY 和 COUNT

GROUP BY & COUNT with multiple parameters

mysql

sql

many-to-many

group-by

count