{keyword}') Union All Select Null,null,null,null,null-- Dyyf < TESTED >

: This command tells the database to combine the results of the original legitimate query with the results of a new query.

The string you provided is a classic example of a . Specifically, this is a Union-based SQL injection attempt. {KEYWORD}') UNION ALL SELECT NULL,NULL,NULL,NULL,NULL-- DyYf

: 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. : This command tells the database to combine