make name type content unique in dns records

database/migrate.go

@@ -59,10 +59,17 @@ func MigrateDNSRecords(dbConn *sql.DB) (*sql.DB, error) {
 		ttl INTEGER NOT NULL,
                 internal BOOLEAN NOT NULL,
 		created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
-		FOREIGN KEY (user_id) REFERENCES users (id) ON DELETE CASCADE);`)
+		FOREIGN KEY (user_id) REFERENCES users (id) ON DELETE CASCADE
+        );`)
 	if err != nil {
 		return dbConn, err
 	}
+
+	_, err = dbConn.Exec(`CREATE UNIQUE INDEX IF NOT EXISTS idx_dns_records_name_content_type ON dns_records (name, type, content);`)
+	if err != nil {
+		return dbConn, err
+	}
+
 	return dbConn, nil
 }