如何在数据库表中查找重复条目？

下面的查询将显示已复制的“书”表中的所有杜威十进制数：如何在数据库表中查找重复条目？

SELECT dewey_number, 
COUNT(dewey_number) AS NumOccurrences 
FROM book 
GROUP BY dewey_number 
HAVING (COUNT(dewey_number) > 1)

然而，我想要做的是有我的查询与显示相关的作者的名字重复的条目（“书”表和“作者”表由“author_id”连接）。换句话说，上述查询将产生以下类似以下

dewey_number | NumOccurrences 
------------------------------ 
5000   | 2 
9090   | 3

我想要什么结果来显示的东西：

author_last_name | dewey_number | NumOccurrences 
------------------------------------------------- 
Smith   | 5000   | 2 
Jones   | 5000   | 2 
Jackson   | 9090   | 3 
Johnson   | 9090   | 3 
Jeffers   | 9090   | 3

任何帮助，您可以提供非常赞赏。而且，如果它起作用，我使用Postgresql DB。

UPDATE请注意，“author_last_name”不在“book”表中。

来源

2009-01-12 Huuuze

重复http://stackoverflow.com/questions/18932/sql-how-can-i-remove-duplicate-rows有人可以关闭吗？ – 2009-01-12 16:28:29

请仔细阅读。这不是重复的。 – Huuuze 2009-01-12 16:41:59

根本不重复。他希望*找到重复的行（以及更多），而不是删除它们。 – 2009-01-12 16:45:03

嵌套查询可以做的工作。

SELECT author_last_name, dewey_number, NumOccurrences 
FROM author INNER JOIN 
    (SELECT author_id, dewey_number, COUNT(dewey_number) AS NumOccurrences 
     FROM book 
     GROUP BY author_id, dewey_number 
     HAVING (COUNT(dewey_number) > 1)) AS duplicates 
ON author.id = duplicates.author_id

（我不知道这是不是达到你想要的最快的方法）

更新：这是我的数据

SELECT * FROM author; 
id | author_last_name 
----+------------------ 
    1 | Fowler 
    2 | Knuth 
    3 | Lang 

SELECT * FROM book; 
id | author_id | dewey_number |   title   
----+-----------+--------------+------------------------ 
    1 |   1 |   600 | Refactoring 
    2 |   1 |   600 | Refactoring 
    3 |   1 |   600 | Analysis Patterns 
    4 |   2 |   600 | TAOCP vol. 1 
    5 |   2 |   600 | TAOCP vol. 1 
    6 |   2 |   600 | TAOCP vol. 2 
    7 |   3 |   500 | Algebra 
    8 |   3 |   500 | Undergraduate Analysis 
    9 |   1 |   600 | Refactoring 
10 |   2 |   500 | Concrete Mathematics 
11 |   2 |   500 | Concrete Mathematics 
12 |   2 |   500 | Concrete Mathematics

这里是的结果上述查询：

author_last_name | dewey_number | numoccurrences 
------------------+--------------+---------------- 
Fowler   |   600 |    4 
Knuth   |   600 |    3 
Knuth   |   500 |    3 
Lang    |   500 |    2

来源

2009-01-12 16:30:05

好吧，可能是一个嵌套的查询是矫枉过正，但现在我确定它的工作原理。 Tony Andrews对author_id专栏的评论也适用于此。 – 2009-01-12 17:07:39

你可能想这

SELECT dewey_number, author_last_name, 
COUNT(dewey_number) AS NumOccurrences 
FROM book 
GROUP BY dewey_number,author_last_name 
HAVING (COUNT(dewey_number) > 1)

来源

2009-01-12 16:25:46 Kibbee

“author_last_name”不在“book”表中。 “书”表和“作者”表通过“book”表中的FKed“author_id”连接。 – Huuuze 2009-01-12 16:27:12

SELECT dewey_number, author_last_name, 
     COUNT(dewey_number) AS NumOccurrences 
FROM book 
JOIN author USING (author_id) 
GROUP BY dewey_number,author_last_name 
HAVING COUNT(dewey_number) > 1

如果书。 AUTHOR_ID可以为空，然后改变连接到：

LEFT OUTER JOIN author USING (author_id)

如果AUTHOR_ID列在每个表不同的名字，那么你不能使用通过，而是使用ON：

JOIN author ON author.id = book.author_id

或

LEFT OUTER JOIN author ON author.id = book.author_id

来源

2009-01-12 16:30:12

select author_name,dewey_number,Num_of_occur 
from author a,(select author_id,dewey_number,count(dewey_number) Num_of_occur 
       from book 
       group by author_id,dewey_number 
       having count(dewey_number) > 1) dup 
where a.author_id = dup.author_id

来源

2015-07-10 18:17:28 user5104009

最简单的方式efective我发现是下面显示：

SELECT 
    p.id 
    , p.full_name 
    , (SELECT count(id) FROM tbl_documents as t where t.person_id = p.id) as rows 
FROM tbl_people as p 
WHERE 
    p.id 
IN (SELECT d.person_id FROM tbl_documents as d 
    GROUP BY d.person_id HAVING count(d.id) > 1) 
ORDER BY 
    p.full_name

来源

2016-03-30 14:12:38

如何在数据库表中查找重复条目？

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