Hi Sasikanth,
The way QlikView stores the data internally that makes difference,fetching data from QVD than Database.
Below example gives accurate picture of how it is done:
If I load a very simple dataset:
Fruit:
LOAD *
INLINE [
Fruit, Color
Banana, Yellow
Blueberry, Blue
Tomato, Red
Tomato, Green
];
And then add both fields as list boxes, I see that there are only 3 fruit listed - even though I have loaded 4 entries. "Tomato" is only stored once by QlikView. Internally, there are binary keys keeping track of the association between "Tomato" along with "Red" and "Green".
In a large data set with a lot of repeating values (especially text values) the fact that each field value is only stored once means that there is a huge saving in the amount of memory needed to store the information. This is why QlikView can store so much data in memory.
Let's add another table of data:Colors:
LOAD * INLINE [
Color, Red, Green, Blue
Yellow, 255, 255, 0
Blue, 0, 0, 255
Red, 255, 0, 0
Green, 0, 255, 0
Amber, 255, 121, 0
];
I now might think that I have 2 tables of data - both of which have a field called "Color". But I don't! There is only one field called "Color" in our dataset and this field will have 5 values. Internally, the association between each of them and their associated values are maintained with binary keys. It just so happens that one of the values - "Amber" - is not associated with any of the values in the "Fruit" field.
Note that there is probably no direct association between "Fruit" and "Red". The association is indirect. However, because of the smaller data set in memory and the binary keys, the association is very fast.
.png "sasikanth"){kind=avatar}
