Database-mysql queries data every two hours.

For example, there are two columns in my database: time and number. I want to query the sum of the data from the initial time "2012-07-110" every two hours. The query result is as follows: 2012-07-110:00:00142012-07-110:00:0022012-07-110:00:0025 .............. And so on. How should I write this command? Hope you can help me. Mysql database

For example, there are two columns in my database: time and number. I want to query the sum of data every two hours after the initial time "01:00:00. The query result is as follows:
03:00:00 14
2012-07-11 05:00:00 2
2012-07-11 07:00:00 25
.............. And so on. How should I write this command? Hope you can help me.