How do I change this query to be a left join?

I've got the query below that I'm using and it's REALLY slow. I've recently learned that a left join would be a lot faster but I don't know how to convert it into a left join.

Anyone have any ideas?

            $PingTrackerSQL = "Select KeywordID from LG.PingTracker where DatePinged > Date_Sub(CurDate(), Interval 7 Day)";

$RKSQL = "select ID from B.Keywords
                                  where RootKeywordID = $RootKeywordID
                                    and ID not in ($PingTrackerSQL)
                                    order by rand() limit 1";

Code (markup):

 

It looks like you can do a regular inner join and set criteria to <= instead of NOT IN >

Something like this:

$RKSQL="select ID from B.Keywords KW
INNER JOIN LG.PingTracker PT ON KW.ID=PT.RootKeywordID
where KW.RootKeywordID = $RootKeywordID
and PT.DatePinged <= Date_Sub(CurDate(), Interval 7 Day)
order by rand() limit 1"

Code (markup):

 

"order by rand()" is what makes your query slow... that and probably a lack of "DatePinged" index...

 

left join won't be faster if you don't try to optimize ORDER BY