Datatype of contact numbers

I follow a very simple rule of thumb to determine the data type.

 

If numeric data is going to be used for an arithmetic operations, then use numeric datatypes, such as, integer, float, smallint, tinyint, bigint, etc. Otherwise use varchar.

 

Probably the only exception to this rule is the primary key column, such as Employee Id, which should be numeric. However, it is for different reason. Primary column (obviously) are member of indexes and column participating on index should, preferably, be numeric because they occupy less space, which in turn increases performance.