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

An attacker (or security researcher) would send this payload to an application to see if it returns an error or a successful response.

For more in-depth technical guides, you can visit the Web Security Academy or community forums like Medium . {KEYWORD}) UNION ALL SELECT NULL,NULL,NULL,NULL,NULL-- ZkhD

: This command combines the result set of the original query with a new set of data. UNION ALL is used instead of UNION because it is often faster and does not remove duplicates, which can be useful for certain types of data extraction. An attacker (or security researcher) would send this

: 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. UNION ALL is used instead of UNION because

The string you provided is a designed to discover the number of columns in a database table. Breakdown of the Payload

: 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.