Summary and Subtasks with Traffic light info

Hi all,

Need some suggestions again.

I have  a table with columns that are sub tasks, another column with summary task the sub task belongs to and another column that has subtask statuses (Red, Amber, Green). 

I need to calculate Summary Task status based on the RAGs/traffic light of subtasks. If a sub task is red then summary is red, if it is not red, but Amber then Amber and if it is not red and Amber, but green then green.

I am not sure how to calculate in sql query and then show it in status report. Any suggestions will be appreciated.

Thanks!