別の列の値であるMySQLselect列

これを試してください：

SELECT id, 
       reason
       CASE
         WHEN reason = 'NoAnswer' THEN NoAnswer
         WHEN reason = 'NetworkBusy' THEN NetworkBusy
       END AS value
FROM table1

次のような出力が得られるはずです：

+----+------------+----------+
| id | reason     | value    |
+----+------------+----------+
|  1 | NoAnswer   |        2 |
+----+------------+----------+