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's another approach:

SELECT
    name,
    min(start_inst) AS start_inst,
    max(end_inst) AS end_inst,
    code,
    subcode
FROM
    (
        SELECT
            A.*,
            COUNT
            (
                CASE WHEN start_inst = previous_end_inst THEN NULL
                ELSE 1
                END
            )
            OVER
            (
                ORDER BY
                    start_inst,
                    name,
                    code,
                    subcode
            ) AS group_number
        FROM
            (
                SELECT
                    name,
                    start_inst,
                    end_inst,
                    LAG
                    (
                      end_inst
                    )
                    OVER
                    (
                        PARTITION BY
                            name,
                            code,
                            subcode
                        ORDER BY
                            start_inst
                    ) AS previous_end_inst,
                    code,
                    subcode
                FROM
                    data
            ) A
        ) B
GROUP BY
    name,
    code,
    subcode,
    group_number
ORDER BY
    group_number

Basically:

1. For each row, subquery A finds the previous end time for the given name, code, and subcode.

2. For each row, subquery B calculates the "group number" -- a running count of preceeding rows (in order of start_inst, name, code, and subcode) where the previous end time calculated in Step 1 is not equal to the start time.

3. The outer query aggregates by group number.

For better or worse, this approach, unlike @stevo's, will create a new "group" if there's a "gap" between the end time of one record and the start time of the next. For example, if you were to create a gap between 12:57 and 13:00 like this...

UPDATE data
SET start_inst = TO_DATE('9/12/2011 13:00', 'MM/DD/YYYY HH24:MI')
WHERE start_inst = TO_DATE('9/12/2011 12:57', 'MM/DD/YYYY HH24:MI');

...the query above would return two rows like this...

NAME                 START_INST       END_INST               CODE    SUBCODE
-------------------- ---------------- ---------------- ---------- ----------
.
.
.
Person1              09/12/2011 12:26 09/12/2011 12:57        161         71
Person1              09/12/2011 13:00 09/12/2011 13:07        161         71
.
.
.

...whereas @stevo's query would return one row like this...

NAME                 START_INST       END_INST               CODE    SUBCODE
-------------------- ---------------- ---------------- ---------- ----------
.
.
.
Person1              12/09/2011 12:26 12/09/2011 13:07        161         71
.
.
.

Hope this helps.