Question

I’d like users to be able to distinguish if they’ve voted for something (by bolding it) or haven’t voted for it yet (not bolded).

For example:

       Voted For Post     Unvoted for
Votes:  77 ↑ ↓             12 ↑ ↓

Here is how my database is set up:

intro

Contains messages

    message_id    intro            user_id      up_vote
     10            Voted For Post   5            77
     11            Unvoted for      5            12

voting

Contains votes

    Voting_id     message_id_fk      user_id
     18             10               5   
     19             10               3     

users

Contains user names

    first_name    user_id
     BOB           5

I don’t know how to properly query the database then make the proper if statement that will distinguish between voted for and unvoted for posts.

Here’s what I have so far:

$sql = mysql_query("SELECT * FROM intro
         INNER JOIN users ON intro.user_id = users.user_id
         ORDER BY `up` DESC ");

echo $row['first_name'] . " " .  $row['intro'];

if( ??? ) {
  echo "<strong>" . $row['up_vote'] . "</strong>";
} else {
  echo $row['up_vote'];
}

Any ideas?

Answer 1

Left join the Voting table and check if any corresponding items were found:

SELECT intro.message_id, intro.intro, intro.user_id, intro.up_vote,
    IF(Voting.user_id IS NULL, 0, 1) AS has_voted
FROM intro
INNER JOIN users ON intro.user_id = users.user_id
LEFT JOIN Voting ON Voting.message_id_fk=intro.message_id
    AND Voting.user_id = 5
ORDER BY `up` DESC 

Then in PHP:

if($row['has_voted'){
    echo "<strong>".$row['up_vote']."</strong>";
}else {
    echo $row['up_vote'];
}

Some explanations:

• Columns from a LEFT JOINed table are NULL if no matching rows were found
• IF() is a function that returns the second parameter if the first parameter evaluates to true, otherwise returns the third parameter. As a function it can be easily used in the SELECT clause
• I replaced SELECT * by explicit selection of the needed columns, which is considered a best practise and in this case necessary because of ambiguous column names
• Of course you will have to replace the literal 5 with your current user id. Use prepared statements or concatenate the query like this: "...Voting.user_id = " . intval($current_user_id) . "..."