Question

我有这两个表，BOOK和REVISION，有点像这样：

Book
Book_ID  |  Book_Name |
======================
1        |      Book 1|
2        |      Book 2|
3        |      Book 3|
4        |      Book 4|

Revision
Rev_Book_ID  |  Date_Modified |
===========================
1            |      10/1/2012   |
2            |      10/3/2012   |
2            |      10/5/2012   |
4            |      10/6/2012   |

当书籍被修改时，书籍的book_id将保存在修订表中。如果该书再次被修改，它将添加该书的另一行。在我的SQL查询中，结果是它显示了本书的2个修订版。

这是我的疑问：

SELECT book.Book_ID, book.Book_Name, Revision.Rev_Book_ID  from Book INNER JOIN Revision ON book.Book_ID=Revision.Rev_Book_ID

还有修订结果（PHP问题）我怎么能实现这个，如果书被修改两次它将显示2个修订或3如果3修订，我知道这是一个if和else但没有想法如何做到这一点。

My Result:

Book ID   |  Book Name     | Revisions        |
==============================================
1         |     Book 1     | 1 Revision       | 
2         |     Book 2     | 2 Revision       | 
2         |     Book 2     | 2 Revision       | 
3         |     Book 3     | No Revision      | 
4         |     Book 4     | 1 Revision       |

Want Result
Book ID   |  Book Name     | Revisions        |
==============================================
1         |     Book 1     | 1 Revision       | 
2         |     Book 2     | 2 Revision       | 
3         |     Book 3     | No Revision      | 
4         |     Book 4     | 1 Revision       |

Answer 1

您可以按book_id进行分组，只选择这些==到MAX（Rev_Book_ID）的rev_book_ids 通常，您希望每本书对数据进行同步。这是mysql规范：http://dev.mysql.com/doc/refman/5.5/en/group-by-functions.html 它应该给你很多想法

Answer 2

对于每本书，您需要修改的数量（COUNT(Date_Modified)）：

   SELECT Book_ID, Book_Name, COUNT(Date_Modified) AS "Revisions"
     FROM Book
LEFT JOIN Revison
       ON Book_ID = Revision_Book_ID
 GROUP BY 1, 2

Answer 3

假设你只是想摆脱重复：

SELECT book.Book_ID, book.Book_Name, Revision.Rev_Book_ID from Book 
INNER JOIN Revision ON book.Book_ID=Revision.Rev_Book_ID GROUP BY book.Book_ID

SQL查询2行，只显示一次具有相同值的行

3 个答案: