How handle NULL in visualization - qliksense

Question

I have two tables (it is example, of course) that I loaded to app from different sources by script
Table 1:
ID
Attribute T1
1
100
3
200
Table 2:
ID
Attribute T2
1
Value 1
2
Value 2
On a list I create table:
ID
Attribute T1
Attribute T2
Finally I have table
ID
Attribute T1
Attribute T2
1
100
Value 1
2
-
Value 2
3
200
-
So, as You know it limits me in filtering and analyzing data, for example I can't show all data that isn't represented in Table 1, or all data for Attribute T1 not equal 100.
I try to use NullAsValue, but it didn't help. Would be appreciate for idea how to manage my case.

Answer 1

To achieve what you're attempting, you'll need to Join or Concatenate your tables. The reason is because Null means something different depending on how the data is loaded.
There's basically two "types" of Null:
"Implied" Null
When you associate several tables in your data model, as you've done in your example, Qlik is essentially treating that as a natural outer join between the tables. But since it's not an actual join that happens when the script executes, the Nulls that arise from data incongruencies (like in your example) are basically implied, since there really is an absence of data there. There's nothing in the data or script that actually says "there are no Attribute T1 values for ID of 2." Because of that, you can't use a function like NullAsValue() or Coalesce() to replace Nulls with another value because those Nulls aren't even there -- there's nothing to actually replace.
The above tables don't have any actual Nulls -- just implied ones from their association and the fact that the ID fields in either table don't have all the same values.
"Realized" Null
If, instead of just using associations, you actually combine the tables using the Join or Concatenate prefixes, then Qlik is forced to actually generate a Null value in the absence of data. Instead of Null being implied, it's actually there in the data model -- it's been realized. In this case, we can actually use functions like NullAsValue() or Coalesce() or Alt() to replace Nulls with another value since we actually have something in our table to replace.
The above joined table has actual Nulls that are realized in the data model, so they can be replaced.
To replace Nulls at that point, you can use the NullAsValue() or Coalesce() functions like this in the Data Load Editor:
table1:
load * inline [
ID , Attribute T1
1 , 100
3 , 200
];
table2:
join load * inline [
ID , Attribute T2
1 , Value 1
2 , Value 2
];
NullAsValue [Attribute T1];
Set NullValue = '-NULL-';
new_table:
NoConcatenate load
ID
, [Attribute T1]
, Coalesce([Attribute T2], '-AlsoNULL-') as [Attribute T2]
Resident table1;
Drop Table table1;
That will result in a table like this:
The Coalesce() and Alt() functions are also available in chart expressions.
Here are some quick links to the things discussed here:
Qlik Null interpretation
Qlik table associations
NullAsValue() function
Coalesce() function
Alt() function