+ ---------- + --------- + --------- + -------- + ------------ + ---------- +
| Field      | Type      | Null      | Key      | Default      | Extra      |
+ ---------- + --------- + --------- + -------- + ------------ + ---------- +
| id         | int(11)   | NO        | PRI      |              | auto_increment |
| date       | datetime  | NO        |          |              |            |
| a          | int(11)   | NO        |          |              |            |
| b          | int(11)   | NO        |          |              |            |
| c          | int(11)   | NO        |          |              |            |
| d          | int(11)   | NO        |          |              |            |
| e          | int(11)   | NO        |          |              |            |
+ ---------- + --------- + --------- + -------- + ------------ + ---------- +
7 rows

select day,hour,c,100.0*(a1/c) as percentage,a1 from
(
    select day(date) as day,hour(date) as hour,count(*) as c, (select count(*) from t where a=1 and hour(date)=hour) as a1 from t group by hour(date)
) as T;

Error Code: 1054. Unknown column 'hour' in 'where clause'