Select rows grouped by keyword but weight each group instead of using COUNT()

Question

I use MySQL database server and I have a table named keywords with the following structure:

kewyord_name | product_id

As well as a list of keywords. I can sort the keywords table based on the list with the following query:

SELECT *, COUNT(*) 
FROM keywords 
WHERE keyword_name IN (comma separated list of keywords) 
GROUP BY product_id 
HAVING COUNT(*) > 2 
ORDER BY COUNT(*) DESC

Is there a way to add weight to the keywords, ie for some of the keywords the COUNT(*) to be increased with more than one?

Answer 1

If you add a column 'weight' to the keywords table you can use Sum(Weight) and Having Sum(Weight) instead of Count(*)...

Edit:

select productid, Sum(weights.weight)
from Keywords
Join (Select 'keyword1' as keyword, 2 as weight
      Union All
      Select 'keyword2' , 5 
      Union All
      Select 'keyword3',  6
) as weights
on Keywords.keyword_name = weights.keyword
group by productid
having Sum(weights.weight) > somevalue
order by weights.weight desc

Answer 2

Using the COUNT(*) function you'll only be able to increment by one with each row. If you want keywords to be treated differently, you could use the SUM() function with a case block.

For example, let's say you have keywords This , that , these . If you want keyword this and that to have a weight of 3, these a weight of 2, and anything else a weight of 1, you can do this:

SELECT keyword_name, 
  SUM(CASE WHEN keyword_name IN ('this', 'that') THEN 3
      WHEN keyword_name IN ('these') THEN 2
      ELSE 1 END) AS weight
FROM myTable
GROUP BY keyword_name;

Here is an SQL Fiddle example.

To match the design of your query you have already, you just need to add your having and order by clauses:

SELECT keyword_name, 
  SUM(CASE WHEN keyword_name IN ('this', 'that') THEN 3
      WHEN keyword_name IN ('these') THEN 2
      ELSE 1 END) AS weight
FROM myTable
GROUP BY keyword_name
HAVING weight > 2
ORDER BY weight DESC;