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

: This is a SQL comment symbol. It tells the database to ignore the rest of the original, legitimate query, effectively "breaking" the intended logic to execute the injected code.

: 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 a SQL comment symbol