Is there a good reason I see VARCHAR(255) used so often (as opposed to another length)?

Question

In multiple courses, books, and jobs, I have seen text fields defined as VARCHAR(255) as kind of the default for \"shortish\" text. Is there any good reason that a length o

Answer 1

0000 0000 -> this is an 8-bit binary number. A digit represents a bit.

You count like so:

0000 0000 → (0)

0000 0001 → (1)

0000 0010 → (2)

0000 0011 → (3)

Each bit can be one of two values: on or off. The total highest number can be represented by multiplication:

2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 - 1 = 255

Or

2^8 - 1. 

We subtract one because the first number is 0.

255 can hold quite a bit (no pun intended) of values.

As we use more bits the max value goes up exponentially. Therefore for many purposes, adding more bits is overkill.