Why does it give me this notice?

Who does:

echo $post['avg']

Give me:

Notice: Undefined index: avg in posts.php on line 39




SELECT p.id, p.message, p.poster, avg(r.rating)
FROM posts p
LEFT OUTER JOIN userpostratings r ON p.id = r.postID
WHERE p.id = 1
GROUP BY p.id

CREATE TABLE IF NOT EXISTS `userpostratings` (
`userID` int(10) NOT NULL DEFAULT '0',
`postID` int(10) unsigned NOT NULL DEFAULT '0',
`rating` int(2) NOT NULL DEFAULT '0',
KEY `userPostRatings_userID` (`use开发者_如何学PythonrID`),
KEY `userPostRatings_postID` (`postID`)
)

CREATE TABLE IF NOT EXISTS `posts` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`message` text,
`poster` int(10) unsigned NOT NULL DEFAULT '0',
`posted` int(10) unsigned NOT NULL DEFAULT '0',
`topic_id` int(10) unsigned NOT NULL DEFAULT '0',
PRIMARY KEY (`id`)
)

The field is named avg(r.rating) not avg.

So $post['avg(r.rating)'] would be correct (assuming you're storing the query results in $post), while $post['avg'] would return a warning, because that index (avg) is never set or defined anywhere.

Use an alias in your query to make the name more friendly, like this:

SELECT p.id, p.message, p.poster, avg(r.rating) AS avg_rating
FROM posts p LEFT OUTER JOIN userpostratings r ON p.id = r.postID WHERE p.id = 1 GROUP BY p.id 

Don't use avg as the alias, since this is a reserved word.

You are getting that notice because the your the avg index in your $post array is not defined. Note, this is not the same as data from your HTTP Post data, $_POST.

As noted the actual field name is "avg(r.rating)" usually its best to Tweak your SQL like so:

SELECT p.id, p.message, p.poster, avg(r.rating) as avgr
FROM posts p
LEFT OUTER JOIN userpostratings r ON p.id = r.postID
WHERE p.id = 1
GROUP BY p.id

Then you can refer to the result of the function with the much more readable"

echo $post['avgr']

Change it to

echo $_POST['avg']