Invalid "IS NOT NULL" part of T-SQL statement

Question

What is wrong with this statement??

SELECT ID, datediff("mi", Start, End) as Total 
FROM TimeTable
WHERE Total is not null

I get an error "Invalid column name"

Answer 1

Reference the expression, not the alias.

SELECT ID, datediff("mi", Start, [End]) as Total 
FROM TimeTable
WHERE datediff("mi", Start, [End])  is not null

EDIT, updated to prevent syntax error for usage of END

Answer 2

Don't use reserved words like "End" as table or column names! Use something like TaskStart/TaskEnd or JobStart/JobEnd or StartDate/EndDate, you'll thanks me everytime you don't have to go back and add [] around your table/column names....