Trying to pull MAX(id) that is NOT NULL

[ripcurlksm]

So this is focused on pulling the "pdf_url" value from the presentation table. I want to pull the newest "pdf_url" for each company, so I am using the MAX() function.

I am using Soda companies as an example. Pepsi, has three urls and I want to pull the newest pdf_url that is not NULL. Coke has one row, but is missing a pdf_url, but my SQL statement is pulling that row as empty. RC Cola, is working fine.

Here is my SQL:

SELECT pdf_url FROM presentation WHERE id = (SELECT MAX(id) FROM presentation WHERE exec_url IS NOT NULL AND id=$value)

Here is my table structure:

company table
=============================
company_id |	name	
=============================
1	   |	Pepsi			
2	   |	Coke
3	   |	RC Cola				
			

presentation table
====================================================
id  |  company_id |   pdf_url 	|  presentation_url
====================================================
1  |	1	  |  file1.pdf  |  pres1.html
2  |	2	  |  NULL       |  pres2.html	
3  |	1	  |  file2.pdf  |  pres3.html	
4  |	3	  |  file3.pdf  |  pres4.html	
5  |	1	  |  NULL	|  pres5.html

With the above SQL I am incorrectly getting these row id's from the presentation table:
2, 4, 5

I want to get the rows from the presentation table:
3, 4

In my SQL it seems like I am not properly filtering out the NULL values, which is causing the issues. Its like I want to "Give me all the rows from the presentation table where pdf_url is not null, then with those results, give me the MAX(id) for each company_id".

[Dan Grossman]

Your query uses some column "exec_url" which isn't in your tables?

Does this work?

SELECT
  pdf_url
FROM
  presentation
WHERE
  id = (SELECT MAX(id) FROM presentation WHERE pdf_url IS NOT NULL GROUP BY company_id)

[ripcurlksm]

Ahh, yea sorry, exec_url is actually pdf_url, I changed it in my examples to be easier to understand...let me try your statement..

[ripcurlksm]

Ok I'm pretty sure I got it! I needed to put IS NOT NULL in both SQL statements like this.

SELECT pdf_url FROM presentation WHERE pdf_url IS NOT NULL AND id = (SELECT MAX(id) FROM presentation WHERE pdf_url IS NOT NULL AND company_id=$value)