Hi Ivan,
Yes the trouble I am having while joining Table A and B, since I want to write 2 join queries for two different columns 
tableC.Col1 takes input from left join of table A and table B
tableC.col2 takes input from left join of table A and table B
Now to get theses columns I have to write two different join queries. I have used database reader to write one left join query , now where can I write the other join query, ? Is there a way if I can write 2 join queries in 1 databse selector node and sum the records?