Question

Im currently creating a voting module for my website, and i have to check if the user voted already, it would just select * from the vote logs, my script inserts a new record for each vote, so say you vote on site 1 its a different record, then say if you voted for site 2.

The columns are site, and the username. I wan’t to be able to check if they voted on all sites based on their username in one php mysql query SELECT * FROM TABLE_NAME

And then sort through the information that way, but i can’t wrap my head around it….

Any help’s appreciated as always!

Answer 1

Here is how I would set it up:

Users table:

CREATE TABLE users(    
    userid    INT UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT,
    username  VARCHAR(50) NOT NULL,
    UNIQUE INDEX(username)
);

Sites table:

CREATE TABLE sites(    
    siteid    INT UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT,
    sitename  VARCHAR(50) NOT NULL,
    UNIQUE INDEX(sitename)
);

Votes table:

CREATE TABLE votes(    
    timestamp timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
    userid INT UNSIGNED NOT NULL,
    siteid INT UNSIGNED NOT NULL,
    UNIQUE INDEX(userid,siteid)
);

When a user casts a vote:

INSERT INTO votes(userid,siteid) VALUES ("$userid","$siteid")

To see what sites a user has voted on:

SELECT sites.sitename FROM sites
INNER JOIN votes ON sites.siteid=votes.voteid
WHERE votes.userid="$userid"

To see what sites a user has NOT voted on (if no rows are returned, then the user has voted on every site):

SELECT sitename FROM sites
WHERE siteid NOT IN (
    SELECT siteid FROM votes WHERE userid="$userid"
)

I like this solution, because then you can display which sites the user has not voted on.

A couple final notes: (1) Never, EVER use “SELECT * FROM table” in a production setting; this is terrible performance. Always select the only the rows you need. And (2) be sure to quote the user input on your queries to avoid SQL injection attacks.