Backup DB before any operation.

wp-import.php

@@ -6,6 +6,9 @@ if ( ! file_exists( 'wp-content/mysql.sql' ) ) {
         return;
 }
 
+// Create backup of the current database.
+echo shell_exec( 'wp db export ./wp-content/mysql-backup.sql' );
+
 $staging_domain = shell_exec( 'wp option get siteurl' );
 echo shell_exec( 'wp db import ./wp-content/mysql.sql' );