I have a simple question about performance and variable caching. Let's suppose I have these two expressions:
Expr1: Sum(Units)
Expr2: Sum(Dollars)
Now, let's suppose I want to calculate a third expressión: Price.
Expr3: Sum(Dollars) / Sum(Units)
As far as I'm concerned, if I want optimum performance I would write the third expression like this:
Expr3: Column(2) / Column(1)
And then, QlikView would just use the previously calculated expressions (Expr1 and Expr2), optimizing performance (labeled aliases would also do the trick).
But what happens if I use variables? Let's suppose this:
Expr1: $(vAmountOfUnits)
Expr2: $(vDollars)
Expr3: $(vDollars) / $(vAmountOfUnits)
In the third expression, would QlikView use the previously cached $(vAmountOfUnits) and $(vDollars)? Or since it's a totally different expression (even if it contains parts of previous ones) it would have to calculate units and dollars again? (Obviously, I know I could go with the Column(x) approach here too, but my real situation is far more complex than this; this is just a very simple example to find out how QlikView deals with variables and caches).
In your example, Expr3: $(vDollars) / $(vAmountOfUnits) will have the same caching as Expr3: Sum(Dollars) / Sum(Units).
When you use dollar expansion on a variable, the expansion itself does not get cached. Once it is expanded, everything is treated as normal. So basically the result of Sum(Units) and Sum(Dollars) will be cached and Sum(Dollars) / Sum(Units) will involve 2 cache lookups. Using variables to store the expressions do not change how caching will be done.
