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

: Calculates the MD5 hash of a specific number. In security testing, this is used as a "canary"—if the database error message displays the calculated hash, the tester knows the injection was successful.

: A function used to query XML data. If given an invalid path (which this payload provides), it throws a database error. : Calculates the MD5 hash of a specific number

: Appends a logical condition. The /**/ is a comment used to bypass simple security filters that block spaces. extractvalue(1, concat(char(126), md5(1002059835))) : If given an invalid path (which this payload

What is SQL Injection? Tutorial & Examples | Web Security Academy : Calculates the MD5 hash of a specific number

: char(126) is the tilde character ( ~ ). The payload attaches this to the start of the data so that the resulting error message clearly displays the extracted value.

This specific payload uses an technique targeting MySQL or MariaDB databases.