Warning: mysql_num_rows() expects parameter 1 to b

问题:

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• mysql_fetch_array()/mysql_fetch_assoc()/mysql_fetch_row()/mysql_num_rows etc… expects parameter 1 to be resource or result 32 answers

I've just changed a site over to a new server, and now I'm getting an error with this code:

<?php 
    $result = mysql_query("SELECT * FROM trends ");
    $num_rows = mysql_num_rows($result);
    echo "<strong>" . $num_rows . "</strong>";
?>

The error is:

Warning: mysql_num_rows() expects parameter 1 to be resource, boolean given.

How can I fix this?

Cheers.

回答1:

Your mysql_query return false if it fails.

"For SELECT, SHOW, DESCRIBE, EXPLAIN and other statements returning resultset, mysql_query() returns a resource on success, or FALSE on error." (http://php.net/manual/en/function.mysql-query.php)

Therefore you need to check if the query failed (which is the case here) before using the result.