Databases Reference
In-Depth Information
The
Left Keep
prefix can also be used, accompanying the
Load
statement corresponding to the
Aircraft Types
dimension table, if the
Main Data
table had been loaded first.
We will now be able to see that when all values from the
Year
listbox are selected, no
aircrafts are being excluded in the
Aircraft Type
listbox.
A solo exercise
Most of the dimensions we loaded to the
Airline Operations
app in
Chapter
2
,
Seeing is Believing
and
Chapter 3
,
Data Sources
present the scenario described
previously. That is, the subset ratio for most key fields in the
Main Data
table
is lower than 100%.
The end users of our QlikView document, HighCloud Airlines, have decided that
they don't need unused values in the dimension tables as it corresponds to either
airlines that are no longer in operation or aircrafts that are no longer in use.
Take what you've learned in this section and reduce all of the dimension tables to
contain only those values that appear in the fact table and save the updated document.
The
Origin and Destination Airports
dimension tables
perform a direct query to the source database. Therefore, the
Exists()
function cannot be used as described here. A QlikView
function might not be interpreted as expected in a direct database
query. Therefore, we need to use the
Left Keep
prefix approach
in those two cases to achieve the expected result.
Once you've reduced the dimension tables and saved the document, take a look at
the size of the QVW file and you'll see the impact of removing unnecessary data.
In this case, the document size on disk will be reduced from around 55 MB to
approximately 33 MB. This will also have a positive impact on RAM usage.
In the next section, we'll work with a side example, so you may now close the
Airline Operations.qvw
document.
