Information density of the field, which indicates the percentage of rows that contain a non-null value
Subset ratio, which shows the percentage of all distinct values for a field in the
table compared to all the distinct values for that field in the entire data model. It is
only relevant for key fields since they are present in multiple tables and do not all
share the same value.
Subset ratios can be used to easily spot problems in key field
associations.
For example, when the combined total of subset ratios for multiple
tables is 100 percent, this may indicate that there are no matching keys between
these tables.
REF: QlikView 11 For Developers..
Let me give you simple example
Sales:
Load * Inline
[
Customer, Sales
A, 100
B, 200
D, 300
];
Customer:
Load * Inline
[
Customer
A
B
C
D
];
If you write above sample script and will check the Table (CTRL + T), you will find two tables.
Sales and Customers
On Sales Table, if you hover the mouse on Customer field, you can see the Subset Ratio is 75% because there is not sales data for Customer C.
Now if you change the script for table Customer like below..
Customer:
Load * Inline
[
Customer
A
B
C
D
]
Where Exists (Customer);
If will not load the Customer C as there are no sales data for the same.
Now check the Subset Ratio. It will be 100%.
If subset ratio is less than 100%, the key is called as Primary Key
but for 100% it is called as Perfect Key.
