PHP: uniqueidentifier

Question

I ‘concat’ an id of just loaded image into mysql user record like this.

 Userid … Photos_ids
 12         1 2 5 7

And this photo_id should be unique. (To create unique file name). Now I get a current last id from memcache. But it's not really safely, as far as I understand.

It there any other ideas? (I do not add any other records into db, so PRIMARY KEY can be used only if I'd add some else special table for this... It's not a good idea).

Answer 1

Have two tables, make the id column the Primary Key and Auto Increment

Example:

CREATE TABLE users(
    id MEDIUMINT UNSIGNED NOT NULL AUTO_INCREMENT,
    name CHAR(60) NOT NULL,
    PRIMARY KEY (id)
);

CREATE TABLE pictures (
     id MEDIUMINT NOT NULL AUTO_INCREMENT,
     name CHAR(30) NOT NULL,
     user_id MEDIUMINT NOT NULL
     PRIMARY KEY (id)
 );

In the example, INSERTing a new pictures would automatically increase the id by 1.

Answer 2

Have a separate table for images.

id (auto-increment)
image_url
..any other info you need about images
user_id (foreign key)

user id obviously shows which user is the owner of that image. It points to the id column of users table. Adjust according to your db model :)

Answer 3

Why not use PHP's uniqid function?