Several posters have made excellent comments about the use of number datatypes
vs. character datatypes for columns that are, or may be, involved in joins.
First off I want to say that join performance should be (one of) the last
considerations in determining the datatype of a column. The datatype should
first and foremost be appropriate for storing the intended content.

In the other posts the predominant gist was
a) test it
b) numbers ought to have an edge as far as performance is concerned

Now let me give you this testcase: