Q: MySQL GROUP BY and remove null rows how am i going to hit my goal? i made an initial query but i can't proceed on how to remove this null/blank rows. i am so grateful if anyone could extend a help. 
this is my query:

this is the result:

but i need to remove all blank/null rows such as this to get my desired result:


A: You want to use conditional aggregation.  Something like:
select . . .,
       max(case when tr.id = 445 then ap.abbreviation end) as `2011-01`,
       . . .

You can use if() instead of case.  I prefer the latter because it is ANSI standard.
AND you need to change the group byclause by removing tr_id.
