Order Results By Occurrence

问题

I have the following two tables.

BookmarkTag ( BookmarkID, TagID ) Tag ( TagID, Title)

Currently I am selecting all the tags with the appropriate BookmarkID. The problem is I want to only select the tag once to avoid duplication in the result and also only bring back the tags the occur the most.

This is my current SQL query:

SELECT Tag.Title 
FROM `Tag` INNER JOIN BookmarkTag 
WHERE BookmarkTag.BookmarkID = 1 AND Tag.TagID = BookmarkTag.TagID'

回答1:

You need to put the join condition in an ON clause after the JOIN keyword. Not in the where clause.
You were mixing SQL89 with SQL92 syntax. This may work I haven't tested, but this is faster.

SELECT Tag.Title 
FROM `Tag` t
INNER JOIN BookmarkTag b ON (t.tagid = b.tagid)
WHERE B.BookmarkID = 1
GROUP BY t.tagid
ORDER BY count(*) DESC

In order to make the results unique per tag, do a group by on tagid.
Then you can order by occurrence by using count(*) to see make the tags with the highest occurrence float to the top.
(try to always use count(*) because it is faster than count(afield) )

回答2:

SELECT t.Title, COUNT(*) AS TitleCount
FROM BookmarkTag AS bt
INNER JOIN Tag AS t ON t.TagID = bt.TagID
GROUP BY t.Title
ORDER BY TitleCount DESC

If You want to get a 7 most popular titles, add LIMIT 7 at the end of query, or any other number. My version will generate all in descending order of their popularity.

来源：https://stackoverflow.com/questions/6324338/order-results-by-occurrence