>Sir, What is the reason of using varchar ?

Copied from the original sample code posted.

Don't use it myself,
the only virtue I know of is that it trims values automatically - simplifies chain concatenation
same storage length though

In this particular case, C(254) should be good enough.

I would even try a M as you don't need any index on this column, and your source data is CSV.

As the file is huge, saving space on disk might also save execution time - to be tested though