Fatal error: Uncaught Error: Call to undefined function mysql_error

I have same issue after creating a backup using duplicator and restoring it on my local machine

Hi Guys!

I had the same problem. According to the mysql specs the function mysql_error was deprecated in PHP 5.5 and removed in PHP 7.0.

See: mysql_error

It’s the revslider plugin that doesn’t conform to the latest API.

I am using one.com and was able to downgrade PHP to version 5.6 in the control panel.

Problem solved!

Downgrading from php 7 to a 5.x version as a fix? Hmmm…there must be a better way.

mysql_error was removed from PHP7.0.0 so best way is change to mysqli_error

please where is db.class.php?

To solve above error, please open file revslider/inc_php/framework/db.class.php and go to line no 29.

You need to replace this code

if(mysql_error()){
	$query = $this->wpdb->last_query;
	$message = $this->wpdb->last_error;

	if($prefix) $message = $prefix.' - <b>'.$message.'</b>';
	if($query) $message .=  '<br>---<br> Query: ' . $query;

	$this->throwError($message);
}

with this one

private function checkForErrors($prefix = ""){
	global $wpdb;
	
	if($wpdb->last_error !== ''){
		$query = $wpdb->last_query;
		$message = $wpdb->last_error;
		
		if($prefix) $message = $prefix.' - <b>'.$message.'</b>';
		if($query) $message .=  '<br>---<br> Query: ' . esc_attr($query);
		
		$this->throwError($message);
	}
}