mysql_num_rows

[zintani]

Hello,

While I was working on my code I faced this problem

(Warning: mysql_num_rows() expects parameter 1 to be resource, boolean given in C:\wamp\www\showlist.php on line 31

Call Stack

# Time Memory Function Location

1 0.0269 371408 {main}( ) ..\showlist.php:0

2 0.0611 383760 mysql_num_rows ( ) ..\showlist.php:31

)

And I tried to figure out why is this message appearing every time I invoke the code. Anyone can help please?

and here is my code

 echo "<br />";
$sql = "SELECT * FROM message, recipientinfo WHERE message.message_id = recipientinfo.mid AND (message.sender = 'kevin.hyatt@enron.com' AND recipientinfo.rvalue = 'michelle.lokay@enron.com' AND recipientinfo.rtype = TO )";
$done = mysql_query ($sql);
$show = mysql_num_rows($done); 
echo $show;

Another question please my database is larger than 500 MB which sometimes I find difficulties when I search using join feature between tables. Is there a method to increase the capability of phpmyadmin?

Thanks a lot

[xyph]

Problem one - use mysql_error()

 

Problem two - get a better server, or optimize your queries/indexes/table structure

[Psycho]

Right, your query is failing. Change your mysql_query() line to this

 $done = mysql_query ($sql) or die("Query:<br>{$query}<br>Error:<br>".mysql_error());

 

However, I see why your query is failing. Here it is in a more readable format:

 $sql = "SELECT *
         FROM message, recipientinfo
         WHERE message.message_id = recipientinfo.mid
           AND (    message.sender = 'kevin.hyatt@enron.com'
                AND recipientinfo.rvalue = 'michelle.lokay@enron.com'
                AND recipientinfo.rtype = TO )";

 

It is failing because of the "TO" in the last condition. If you are trying to compare against a string then the value need to be in single quotes: 'TO'. If TO is a variable or constant then you will need to define it appropriately - if it is a string then it still needs to be in quotes. Personally I prefer to use explicit joins. I don't know if it is more efficient, but it is easier to see the relationships.

 

This is how I would have prepared that query

 $sql = "SELECT *

         FROM message
         JOIN recipientinfo
           ON message.message_id = recipientinfo.mid

         WHERE message.sender = 'kevin.hyatt@enron.com'
           AND recipientinfo.rvalue = 'michelle.lokay@enron.com'
           AND recipientinfo.rtype = 'TO'";

 

Don't be afraid to add line breaks and spacing to your code. It makes the code much, much more readable and logical for a human.

 

[zintani]

Thanks a lot that helps me to go through.