What is the main difference between a "Normal" SQL Injection and a "Blind" SQL Injection vulnerability?

Request visibility to the application administrator is unrelated to the distinction between normal and blind SQL Injection; both attack types generate server-side requests that can appear in logs.

Blind SQL Injection does not mean the application properly filters input; the input is still processed by the database, but results are simply not reflected in the response.

The defining characteristic is that error information is hidden from the attacker, not from the administrator; the administrator may still see errors in server logs while the attacker sees none.

In a normal SQL Injection, the application reflects error messages or query output directly in the HTTP response, allowing the attacker to see injection results immediately. In Blind SQL Injection, the application suppresses error details and does not display query results, so the attacker must infer database information by observing indirect behavioral differences - such as true/false response variations (Boolean-based) or measurable time delays (time-based). This absence of visible feedback defines the 'blind' classification.