Inferential SQL injection is also commonly known as blind SQL injection; it is referred to as so because, in this case, the data is not actually transferred between the web application and the attacker is not able to directly see the response of the injected queries. Instead, this kind of vulnerability is exploited when the attacker enumerates the database by observing the application's behavior. There are two kinds of blind SQL injection:

• Boolean-based blind SQLi: This is a type of inferential SQL injection attack in which the attacker mainly sends an SQL query to the database, in response to which the application returns results that depend on whether the query is a true or false result
• Time-based blind SQLi: In time-based SQL injection the attacker relies on sending an SQL query to the database; the result, either true or false, is based on a time delay for the response that is returned back from the database