Lets say I have such a table:

id|time|operation
1  2      read
2  5      write
3  3      read
4  7      read
5  2      save
6  1      open

and now I would like to do two things:

1. Divide all these records into two groups: 1) all rows where operation equals to "read" 2) all other rows.
2. Sum the time in each group.

So that my query would result only into two rows.

What I got so far is:

select 
 sum(time) as total_time,
 operation
group by
 operation
;

Although that gives me many groups, depending on the number of distinct operations.

How I could group them only into two categories?

Cheers!