SQL field value help - Cemetech | Forum

TsukasaZX · 22 May 2008 02:42:28 pm

Okay, so I'm creating an SQL database to run an archive system off of, but I'm somewhat confused as to what a couple things mean:

What does the Null option mean? what is it used for?

What is the difference between an empty default value and a "NULL" one?

what is "unsigned"?

Yes, I'm googling this, but I can't seem to find much.

elfprince13 · 22 May 2008 04:21:44 pm

unsigned means whether it can't hold negative values.

KermMartian · 22 May 2008 04:47:50 pm

Third line in the second Google result: http://en.wikipedia.org/wiki/Unsigned
Null means a blank entry, ie, not only zero, but no value whatsoever.

TsukasaZX · 22 May 2008 04:56:10 pm

Okay, didn't think to search just for "unsigned" >>;;
Anywho, the wiki article helped. I suppose it's best to have archive db fields unsigned.

As for NULL, I still don't understand what it's USEFUL for in an SQL database. Confused

Is it better to have fields that will be user-defined set to be NULL?

KermMartian · 22 May 2008 05:26:48 pm

NULL is useful if you want to be able to distinguish between a field that has not been set to anything yet, and a field that has been set to zero.

TsukasaZX · 22 May 2008 05:41:03 pm

ah, so whether it's Null or Not Null wouldn't really matter in the case of an archives database since the fields wouldn't be changed beyond initial user definition.

Also, one last question:

What's the point of "Unique" and "Index"? I know "Primary" would be the main field that has to have defined values, but the others I don't know.

elfprince13 · 22 May 2008 05:44:18 pm

unique columns can't have multiple instances of the same value between rows

an index is an auto incrementing column

TsukasaZX · 22 May 2008 05:48:05 pm

Ah, but under phpMyAdmin, I can only choose one of the three and "auto_increment" is a choice under "extra"