: The attacker is trying to determine how many columns the original database table has. By providing five NULL values, they are testing if the original query also returns five columns (the number of columns must match for a UNION to work).
: This is the SQL comment syntax. It tells the database to ignore everything that follows it, which prevents the remaining "real" code from causing a syntax error. {KEYWORD}') UNION ALL SELECT NULL,NULL,NULL,NULL,NULL-- DyYf
: This command tells the database to combine the results of the original legitimate query with the results of a new query. : The attacker is trying to determine how
: This is likely a "fingerprint" or a random string used by automated security scanners (like Burp Suite or SQLmap) to identify which specific payload successfully triggered a response. Why you are seeing this It tells the database to ignore everything that
The string you provided is a classic example of a . Specifically, this is a Union-based SQL injection attempt.
If you found this in a product review section, a log file, or a search bar, it means someone (or an automated bot) was . They were checking if the site properly "sanitizes" user input or if it is vulnerable to data theft.