SQL invalid Identifier query

I am getting an error that grandvisit is an invalid identifier, and I am unsure if I will get it with other identifiers either. Any light shed on this would be amazing. As I cannot see why it differents from others.

Answer

You cannot refer the alias names in same select clause where it is generated.

SELECT Sum(aerosolvisit + hazvisit + hvvisit + hlopvisit
           + plvisit + miniloadvisit + aprvisit + apr2visit
           + aprawkvisit) AS grandvisit 

To calculate grandratio you are using the below expression which uses the alias name grandvisit

SELECT CASE
         WHEN Sum(grandtotal) = 0 THEN 0
         WHEN Sum(grandvisit) = 0 THEN 0
         ELSE Sum(grandtotal) / Sum(grandvisit)
       END AS grandratio 

You can use derived table to do this

SELECT CASE
         WHEN Sum(grandtotal) = 0 THEN 0
         WHEN Sum(grandvisit) = 0 THEN 0
         ELSE Sum(grandtotal) / Sum(grandvisit)
       END AS grandratio 
From 
(
SELECT Sum(aerosolvisit + hazvisit + hvvisit + hlopvisit
           + plvisit + miniloadvisit + aprvisit + apr2visit
           + aprawkvisit) AS grandvisit 
 ...
) A

Note : You are using old style outer join’s(+=). It is better to use Right/Left joins which is more readable