{keyword}) Union All Select Null,null,null,null,null-- Zkhd -

: This is likely a random string or a "signature" used by a vulnerability scanner (like Burp Suite or sqlmap) to track if the payload was successfully reflected in the application's response.

: This part attempts to break out of the existing SQL query structure. The closing parenthesis ) is used to "close" a likely function or subquery in the application's original code. {KEYWORD}) UNION ALL SELECT NULL,NULL,NULL,NULL,NULL-- ZkhD

: This is a comment indicator that tells the database to ignore the rest of the original query that follows. : This is likely a random string or

: The attacker uses a specific number of NULL values to match the number of columns in the original query's SELECT statement. NULL is used because it is compatible with almost any data type (strings, integers, dates), maximizing the chance that the injected query will succeed. : This is a comment indicator that tells

: The original table has exactly 5 columns. This confirms a vulnerability and allows the attacker to move to the next step: identifying which columns can display sensitive data.