Caching variables

[ramonarcusa36]

Hey guys.

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).

Thanks in advance!

[mikevwang]

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.