int(11) vs. int(anything else)

Question

I'm new to web programming and doing different tutorials that I can find on the net.

I did my research and found out that in int(11), 11 is the maximum display width for integers and it's the default value if unless the integer is UNSIGNED (in this case it's 10).

When I see something like this:

id INT(11) not null AUTO_INCREMENT 

I have no questions. But why do I see different things in different tutorials? For examlpe, in some, it says,

id INT(10) not null AUTO_INCREMENT 

And even

id INT(4) not null AUTO_INCREMENT 

What are the authors of those tuts trying to achieve? None of them seem to bother to give an explanation what 10 or 4 means.

Alright, they're obviously reducing the display width, but why? What's wrong with the default width of 11? Why would they want to change it? Or are there any other reasons I don't know of?

Thanks.

Answer 1

The x in INT(x) has nothing to do with space requirements or any other performance issues, it's really just the display width. Generally setting the display widths to a reasonable value is mostly useful with the UNSIGNED ZEROFILL option.

//INT(4) UNSIGNED ZEROFILL 0001 0002  ... 0099 ... 0999 ... 9999 ... 10000  //INT(2) UNSIGNED ZEROFILL 01 02  ... 09 ... 99 ... 100 

Without the UNSIGNED ZEROFILL option the value will be left-padded with spaces to the appropriate display width.

//INT(4)    1    2  ...   99 ...  999 ... 9999 ... 10000  //INT(2)  1  2  ...  9 ... 99 ... 100