{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.

For more in-depth technical guides, you can visit the Web Security Academy or community forums like Medium .

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

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

: The number of NULL values (5 in this case) does not match the number of columns in the original table.

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

: 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.