MYSQL enumeration: @rownum, odd and even records

(sorry dunno how to delete this post as I have got the answer already)

Hi,

I asked a question about creating temporary/ virtual ids for query results,

There is a Standard PHP Library/ SPL solution to my problem, but I found another solution from this link below,
http://craftycodeblog.com/2010/09/13/rownum-simulation-with-mysql/

I have managed to enumerate each row,

SELECT 
    u.pg_id AS ID, 
    u.pg_url AS URL,
    u.pg_title AS Title,
    u.pg_content_1 AS Content,
    @rownum:=@rownum+1 AS rownum
    
    FROM (
    	SELECT pg_id, pg_url,pg_title,pg_content_1
    	FROM root_pages
    	
    	WHERE root_pages.parent_id = '7'
    	AND root_pages.pg_id != '7'
    	AND root_pages.pg_cat_id = '2'
    	AND root_pages.pg_hide != '1'
    	
    	ORDER BY pg_created DESC
    ) u,
    
    (SELECT @rownum:=0) r

result,

   ID 	URL 	Title 	Content 	rownum
    53 	a       x       x 	        1
    52 	b       x       x 	        2
    43 	c       x       x        	3
    41 	d       x       x       	4

but how can I work on it a bit further - I want to display the odd or even records only like the ones below - is it possible?

odd records,

   ID 	URL 	Title 	Content 	rownum
    53 	a       x       x 	        1
    43 	c       x       x        	3

even records,

    ID 	URL 	Title 	Content 	rownum
    52 	b       x       x 	        2
    41 	d       x       x       	4

thank you.

p.s. I don’t quite understand the sql query actually even though I almost got the anwer, for instance, what do the ‘u’ and ‘t’ mean?