将多个SUM查询合并为一个结果

So.... we have three different tables that pertains to a contest in which the DB keeps track of how many points they've received for each contest. Contest 1, 2 and 3. Each time that user achieves something, a new row is created for that user with the additional points. So in order to calculate all the points that user has received I use a select sumSo.... we have three different tables that pert