Auto Expanding VLOOKUP Table Array
Ok, this time I want to talk about how to create a vlookup table array that automatically expanding in accordance with the numbers of available data.
As we know, the basic form of Excel VLOOKUP to look for A1 value in range B1:D15 column no 2 is like this:
=VLOOKUP(A1,B1:D15,2)
With parameters such as the value we looking for, range of table array where we would like to find the value that we want, and how far the column of values that we want from the left most column of the table array range.
Unfortunately, this form is rigid, the table array range is fixed to row 6 until row number 3450. So this form is not suitable for doing VLOOKUP on the database which always dynamic, increase or decrease from time to time.
Using the above VLOOKUP form, every time there is an addition of new data, we need to change the VLOOKUP formula to match the numbers of expanding data.
We need to change the format of the VLOOKUP formula to be more flexible and save the time we need to manually adjust the formula by hand.
The following changes is the form that we need:
=VLOOKUP($A1,OFFSET($B$1,0,0,COUNTA($B:$B),3),2)
Here we got help from OFFSET Excel function to return the reference of VLOOKUP table array range that we need plus the COUNTA function to calculate the maximum number of rows on the database.
This way, every time there are any reduction or addition of new data on the VLOOKUP table array, COUNTA will return the number of rows needed, and OFFSET will provide the referense of the new table array, so we do not need to make changes the formula manually 
Read this great article of Dynamic Ranges for more information about dynamic ranges in Excel.
I am confess, I can not write well, let alone give an easy to read and easy to understand explaination 
