Combine rows when the end time of one is the start time of another (Oracle)

Question

I just can\'t seem to get this query figured out. I need to combine rows of time-consecutive states into a single state.

This question is similar to the question fou

Answer 1

Here is a solution using a recursive query instead of analytic functions (as suggested by @wildplasser):

SELECT   name, code, subcode, MIN(start_inst) AS start_inst, MAX(end_inst) AS end_inst
FROM     (SELECT     name,
                     start_inst,
                     end_inst,
                     code,
                     subcode,
                     MIN(CONNECT_BY_ROOT (start_inst)) AS root_start
          FROM       data d
          CONNECT BY PRIOR name = name 
                 AND PRIOR end_inst = start_inst 
                 AND PRIOR code = code 
                 AND PRIOR subcode = subcode
          GROUP BY   name, start_inst, end_inst, code, subcode)
GROUP BY name, code, subcode, root_start;

The connect by clause in the innermost query causes the data to be returned in a hierarchical fashion. connect_by_root gives us the value at the root of each branch. Because we don't have a good candidate for a start with clause, we'll get all child rows (where end_inst equals another row's start_inst and all other columns are the same) multiple times: once as a root and once (or more) as a branch. Taking the min of the root eliminates these extra rows while giving us a value to group on in the outer query.

In the outer query, we perform another group by to consolidate the rows. The difference is that, in this case, we have root_start there as well to identify which rows are consecutive and therefore need to be consolidated.