Mega'and/**/extractvalue(1,concat(char(126),md5(1002059835)))and' -

: A function used to query XML data. If given an invalid path (which this payload provides), it throws a database error.

: Appends a logical condition. The /**/ is a comment used to bypass simple security filters that block spaces. extractvalue(1, concat(char(126), md5(1002059835))) : : A function used to query XML data

: Attempts to balance the trailing single quote of the original query to prevent a syntax error that might stop the script from running. Context of Use : A function used to query XML data

The string you've provided is an example of a used in automated vulnerability scanning or attacks. It is not a legitimate "proper feature" of a software application; rather, it is designed to exploit security flaws in a database's error-handling mechanism. Breakdown of the Payload : A function used to query XML data