添加两个表值与当前日期（今天日期）

Question

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.

Answer 1

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.