The string you provided is a designed to discover the number of columns in a database table. Breakdown of the Payload
: 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. {KEYWORD}) UNION ALL SELECT NULL,NULL,NULL,NULL,NULL-- ZkhD
: 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