添加两个表值与当前日期(今天日期)

I was trying to add sum of Total value from different tables. It's sucess with this query But I want addition of current date.

Table1                       Table2
Date     Total_Cost     Date     Total_Cost
21/01/2015     500     21/01/2015     500

SELECT (SELECT SUM(Total_Cost) FROM Table1) + (SELECT SUM(Total_Cost) FROM Table2) as total

Its Give proper answer : 1000

But I Run this Query Addition With Current Date.

SELECT (SELECT SUM(Total_Cost) FROM Table1 WHERE DATE =  CURDATE()) + (SELECT SUM(Total_Cost) FROM Table2 WHERE DATE =  CURDATE()) as total

Its Give Value :NULL

Please help me someone To solve this thank you in advance.

Your query needs to cope with the possibility that no rows may be returned by either of your select statements (ie a NULL value) by using ISNULL eg

ISNULL(SELECT SUM(X) FROM Table1 WHERE Date=CURDATE(),0.0) 

or even:

SELECT ISNULL(SUM(Total_Cost),0.0) FROM 
(
  SELECT Total_Cost FROM Table1 WHERE Date = CURDATE()
  UNION ALL
  SELECT Total_Cost FROM Table2 WHERE Date = CURDATE()
) S1

Apologies if this is not valid MySQL syntax I'm more familiar with SQL Server, but I hope it helps even so.