{keyword} Union All Select Null,null,null,null,null,null,null,null-- Ppsq Online

Once an attacker knows there are 8 columns, they can replace the NULL values with commands to extract sensitive data, such as usernames, passwords, or database versions. SQL injection UNION attacks | Web Security Academy

The primary goal of this specific syntax is to returned by the original, legitimate database query. Once an attacker knows there are 8 columns,

: Attackers use NULL because it is compatible with almost every data type (integers, strings, dates), making it the "safest" way to avoid syntax errors while testing column counts. such as usernames