Blank values in SQL statement

[Mojster]

This works OK:

SELECT A.Num-A.Num2
FROM "Test.DB" A, "test2.DB" B


But why this SQL statement return as resault NULL if Num (or Num2) is blank? What is the solution of this problem?

SELECT A.Num-A.Num2
FROM "Test.DB" A, "test2.DB" B
WHERE A.X=B.X

 

[vecjjk]

If num and num2 are integers, a blank is probably a null. Using null in an expression always yields null. If you want a "blank" (null) to act like zero, you can try this . . .

SELECT NVL(A.Num,0)-NVL(A.Num2,0)
FROM "Test.DB" A, "test2.DB" B
WHERE A.X=B.X