Question

Let’s say I have four tables: PAGE, USER, TAG, and PAGE-TAG:

Table      | Fields ------------------------------------------ PAGE       | ID, CONTENT TAG        | ID, NAME USER       | ID, NAME     PAGE-TAG   | ID, PAGE-ID, TAG-ID, USER-ID 

And let’s say I have four pages:

PAGE#1 'Content page 1' tagged with tag#1 by user1, tagged with tag#1 by user2  PAGE#2 'Content page 2' tagged with tag#3 by user2, tagged by tag#1 by user2, tagged by tag#8 by user1   PAGE#3 'Content page 3' tagged with tag#7 by user#1 PAGE#4 'Content page 4' tagged with tag#1 by user1, tagged with tag#8 by user1 

I expect my query to look something like this:

select page.content ? from page, page-tag  where  page.id = page-tag.pag-id  and page-tag.tag-id in (1, 3, 8)  order by ? desc 

I would like to get output like this:

Content page 2, 3 Content page 4, 2 Content page 1, 1 

---

Quoting Neall

Your question is a bit confusing. Do you want to get the number of times each page has been tagged?

No

The number of times each page has gotten each tag?

No

The number of unique users that have tagged a page?

No

The number of unique users that have tagged each page with each tag?

No

I want to know how many of the passed tags appear in a particular page, not just if any of the tags appear.

SQL IN works like an boolean operator OR. If a page was tagged with any value within the IN Clause then it returns true. I would like to know how many of the values inside of the IN clause return true.

Below i show, the output i expect:

page 1 | in (1,2)   -> 1  page 1 | in (1,2,3) -> 1  page 1 | in (1)     -> 1  page 1 | in (1,3,8) -> 1  page 2 | in (1,2)   -> 1  page 2 | in (1,2,3) -> 2  page 2 | in (1)     -> 1  page 2 | in (1,3,8) -> 3  page 4 | in (1,2,3) -> 1  page 4 | in (1,2,3) -> 1  page 4 | in (1)     -> 1  page 4 | in (1,3,8) -> 2 

This will be the content of the page-tag table i mentioned before:

   id       page-id  tag-id  user-id        1       1        1       1       2       1        1       2       3       2        3       2       4       2        1       2       5       2        8       1       6       3        7       1       7       4        1       1       8       4        8       1  

@Kristof does not exactly what i am searching for but thanks anyway.

@Daren If i execute you code i get the next error:

#1054 - Unknown column 'page-tag.tag-id' in 'having clause'  

@Eduardo Molteni Your answer does not give the output in the question but:

Content page 2 8 Content page 4 8 content page 2 3 content page 1 1 content page 1 1 content page 2 1 cotnent page 4 1 

@Keith I am using plain SQL not T-SQL and i am not familiar with T-SQL, so i do not know how your query translate to plain SQL.

Any more ideas?

Answer 1

OK, so the key difference between this and kristof’s answer is that you only want a count of 1 to show against page 1, because it has been tagged only with one tag from the set (even though two separate users both tagged it).

I would suggest this:

SELECT page.ID, page.content, count(*) AS uniquetags FROM    (  SELECT DISTINCT page.content, page.ID, page-tag.tag-id        FROM page INNER JOIN page-tag ON page.ID=page-tag.page-ID        WHERE page-tag.tag-id IN (1, 3, 8)     )     GROUP BY page.ID 

I don’t have a SQL Server installation to check this, so apologies if there’s a syntax mistake. But semantically I think this is what you need.

This may not give the output in descending order of number of tags, but try adding:

      ORDER BY uniquetags DESC 

at the end. My uncertainty is whether you can use ORDER BY outside of grouping in SQL Server. If not, then you may need to nest the whole thing in another SELECT.