isnull

------解决方案--------------------
select a.* , isnull(b.col , 0)
from a left join b on a.id = b.id

------解决方案--------------------
SQL code
SELECT    
  A.ID, A.userID, A.PlanName, A.Count, ISNULL(B.clickCount,0),ISNULL( B.clickMoneyCount,0) 
FROM  
  dbo.Plan AS A 
LEFT JOIN
  (SELECT  SUM(clickCount) AS clickCount, SUM(clickMoneyCount) AS clickMoneyCount, ID 
FROM    
  dbo.Click  GROUP BY ID) AS B ON A.ID = B.ID

------解决方案--------------------
探讨

SQL codeSELECT    
  A.ID, A.userID, A.PlanName, A.Count,ISNULL(B.clickCount,0),ISNULL( B.clickMoneyCount,0)FROM  
  dbo.PlanAS ALEFTJOIN
  (SELECTSUM(clickCount)AS clickCount,SUM(clickMoneyCount)AS clickMoneyCount, IDFROM    
  dbo.ClickGROUPBY ID)AS BON A.ID= B.ID