Issue in get duplicate value in sum query sqlite

hello friends i have 2 tables like below

tab_a --> "unit_info_id"   ,"unit_id"  ,"p_id"   ,"p_bathroom"  ,"p_bedroom"  ,"p_size"  ,"p_rent"  ,"p_isrent"  ,"u_note"  ,"r_id"  , "isactive"  

tab_b-->   "rent_id"   ,"unit_info_id"   ,"t_id"  ,"rent_amount"  ,"rent_note"  ,"rent_date"  ,"rent_time"  ,    "r_id" 

and my query is as below

SELECT a.* ,
 (SELECT   SUM(rent_amount)
 FROM tab_b
 LEFT JOIN  tab_a ON tab_b.unit_info_id = tab_a.unit_info_id
 WHERE    tab_b.rent_date 
 between  '2015-02-03' and '2015-12-03'
GROUP BY tab_b.unit_info_id
  ) AS "TotalIncome" 
FROM tab_a  a ,tab_b b
WHERE a.r_id=1 group by a.unit_info_id

when i run above query it gave me duplicate value in totalIncome alias like below image

as per my current data i have rent_amount only for unit_id =1 , in unit_id=2 and unit_id=3 there are no any data in my tab_2 table but when i run above query it gave me output something like above image i need totalIncome as per particular unitwise so any idea how can i solve it?