The $wpdb
object has some properties getting set for that:
global $wpdb;
// Print last SQL query string
echo $wpdb->last_query;
// Print last SQL query result
echo $wpdb->last_result;
// Print last SQL query Error
echo $wpdb->last_error;
Note: First of all you have to set define( 'SAVEQUERIES', true );
in your wp-config.php
file at root folder of WordPress.