what does unique id exactly do?

[ceanth]

create table items
(
itemId int auto_increment not null,
itemName varchar(50),
itemDesc varchar(250),
itemPrice decimal(4,2),
primary key(itemId),
unique id(itemId)
);

what does the "unique id" field in this table do? would the table function differently without this field, if so how?

[jpmoriarty]

i think it's just a flag to tell the db that the field is a unique id - that's guaranteed by the auto_increment thing, but i think the db uses it as a check when it's running a query. It's easier to check the db schema to see which fields are unique than to check each field and see if it's an auto_increment.

If you see what i mean

[trooper]

The other use for unique id is to put some logic into the db.

By having a field as unique then no other record in that table can have the same value in that field.

Know your logic very well before adding unique id as a key!

HTH

GM