In Summary
To help ensure this, the calculation of the hash
function should INVOLVE THE ENTIRE
SEARCH KEY and not just a portion of the
key.
For example, computing a modulo of the entire
ID number is much safer than using only its
first two digits.
And, if you do use modulo arithmetic, the Table
size should be a prime number.
This takes care of cases where search keys are
multiples of one another.