All Select Null,null,null,null-- Uizf | {keyword} Union

: This is likely a random string used as a unique identifier or "signature" to help the attacker find their specific test result in a large log file or report. Purpose of Such a Payload Attackers use this technique to:

: The attacker is attempting to determine the number of columns returned by the original database query. By adding NULL values until the page loads without an error, they can identify the table's structure. {KEYWORD} UNION ALL SELECT NULL,NULL,NULL,NULL-- Uizf

: Confirm that the application is vulnerable to SQL injection. : This is likely a random string used