MySQL与PHP的联接查询

Question

table: database1.comment
id | owner_id | comment    
1  |  1       | some words 
2  |  1       | some words
3  |  2       | some words

table: database2.users
id | display_name
1  | admin    
2  | guest

I am try to join 2 tables query, here is my php code:

$result = mysql_query("SELECT * FROM database1.comment INNER JOIN database2.users ON database1.comment.owner_id=database2.users.id order by database1.comment.id DESC");
while ($row = mysql_fetch_array($result)){
     echo '<li>'.$row['display_name'].': '.$row['comment'].'</li>';
}

I get a error message: Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given . How to make a work code ( optimize way )

Answer 1

If your query is invalid (or otherwise "failed"), mysql_query() returns "false" (instead of an array).

SUGGESTIONS:

1. Cut/paste your SQL string into MySQL, see what's incorrect, and fix it. And that point, your PHP should be OK.

2. Check your result (and gracefully handle any failures/errors) in your code:

EXAMPLE (error: no "from" clause):

$result = mysql_query('SELECT * WHERE 1=1');
if (!$result) {
    die('Invalid query: ' . mysql_error());
}

Answer 2

mysql_query return resource on success and boolen false on failure when there is no results.

http://php.net/manual/en/function.mysql-query.php