sql查询某个小时段的数据

mysql> select EXTRACT(HOUR FROM createdate) as hour, count(*) as count from user where left(createdate,10)='2006-03-30' group by hour;
+------+-------+
| hour | count |
+------+-------+
|    0 |   779 |
|    1 |   909 |
|    2 |   488 |
|    3 |   189 |
|    4 |   170 |
|    5 |   285 |
...
...