Question

这是原始数据

Book | Author | Year

A    | A1     | 1985

A    | B1     | 1985

B    | A1     | 1988

B    | C1     | 1988

D    | A1     | 1990

D    | C1     | 1990

D    | B1     | 1990

以下是我要找的输出，

Author1 | Author2 | year | count

A1      | B1      | 1985 | 1

A1      | C1      | 1985 | 1

A1      | C1      | 1988 | 1

A1      | B1      | 1990 | 1

A1      | C1      | 1990 | 1

B1      | C1      | 1990 | 1

非常感谢任何帮助。感谢

Answer 1

SELECT A.author AS author1, 
       B.author AS author2,
       A.year,
       COUNT(*) AS "count"
  FROM Author A
       LEFT JOIN Author B
          ON B.book = A.Book
          AND B.author > A.Author
       GROUP BY A.author, B.author, A.year
       ORDER BY A.author, B.author, A.year

只要Author表中每本书的行数不超过两行，这样就可以正常工作。否则，它将为每本书产生多行。如果可能出现这种情况，则应指出应使用哪种SQL风格，因为限制表B结果的方法因实现而异。我已经任意选择按字母顺序列出作者，因为似乎没有指出哪个作者是“主要的”。

我希望表中还有其他列，你没有告诉我们 - 最具体的是一个主键，也许还有一些属性表明了作者关于给定书籍的“计费顺序”。

如果可能的话，您可能需要重新考虑您的表格设计：它采用非规范化形式，使数据完整性难以执行。

Answer 2

您正在寻找的查询是具有聚合的自联接：

select t1.author as author1, t2.author as author2, t1.year, count(*) as `count`
from t t1 join
     t t2
     on t1.book = t2.book and
        t1.author < t2.author
group by t1.author, t2.author, t1.year
order by t1.author, year;

使用sql汇总三个变量

2 个答案: