PHP query multiple Tables - php

Question

I'm having trouble getting any information to display from this query. Anyone know where I'm going wrong?
Thank you!
$query = "SELECT * ".
"FROM comments, users ".
"WHERE comments.user_id = users.user_id ".
"ORDER BY comments.date DESC ".
"LIMIT 10";
$result = mysql_query($query) or die(mysql_error());
while ($row = mysql_fetch_array($result)) {
echo $row['users.user_id'];
echo $row['comments.comment'];
}

Answer 1

use mysql_fetch_assoc() instead of mysql_fetch_array().
In your loop use the column name as the array key:
while ($row = mysql_fetch_assoc($result)) {
echo $row['column_name1'];
echo $row['column_name1'];
}
In your query try to be more specific on the select statement, try not to use *.

Answer 2

You're probably getting the error because you are sorting (ORDER BY) on a field that does not exist in your query.
It would be best practice to not use the "SELECT *" querying. If all you need are specific values, specify them. This also helps when retrieving the data...
$query = "SELECT users.user_id, comments.comment, comments.date ".
"FROM comments, users ".
"WHERE comments.user_id = users.user_id ".
"ORDER BY comments.date DESC ".
"LIMIT 10";
$result = mysql_query($query) or die(mysql_error());
while ($row = mysql_fetch_array($result)) {
echo $row['user_id'];
echo $row['comment'];
echo $row['date'];
}

Answer 3

It is good practice to specify column names in a query rather than using * - on some DBs there is a performance impact and on all it prevents any unexpected behaviour cropping up from table changes.
In the example I think the issue is arsing from the array keys you are using - you don't need to include the table name in them, just the column name:
echo $row['user_id'];
echo $row['comment'];

Answer 4

The better practice is to write only fields what you need in your sql query like this:
$query = "SELECT u.user_id uid, c.comment comment ".
"FROM comments c, users u ".
"WHERE comments.user_id = users.user_id ".
"ORDER BY comments.date DESC ".
"LIMIT 10";
Using so type of queries you reduce the time of executing your query and transmitting data from database server to your php script. After this modification your cycle transformed to:
while ($row = mysql_fetch_array($result)) {
echo $row['uid'], $row['comment'];
}

Answer 5

I use PDO method but this can work for you too:
<?php
$sql = "SELECT * FROM comments as c INNER JOIN users as u ON c.user_id=u.user_id WHERE u.user_id=:user_id ORDER BY c.date DESC LIMIT 10";
//prepare the connection to database
$prep = $conn->prepare($sql);
//change the parameters for user_id on WHERE condition you can put anything you want but i will put the user session id
$prep->bindParam(":user_id", $_SESSION['user_id']);
$prep->execute();
//ill use fetchAll function because it can be more than 1 comment
$datas = $prep->fetchAll();
foreach($datas as $data){
echo $data['user_id'];
echo $data['comment'];
echo $data['date'];
}
?>