Hi Krishna,
You should perform "Left outer JOIN NNM1 ON NNM1.Series =OINV.Series and NNM1.ObjectCode=OINV.ObjType" in From clause.
Also in select clause you should take this in consideration as LEFT(NNM1.SeriesName,2) as Inv_type
I hope this may solve your problem.
Regards,
Harshal Makwana