How to Find Minimum and Maximum Time Intervals for Consecutive Events with Gaps and Islands?

Finding Minimum and Maximum for Consecutive Rows with Gaps and Islands

In the context of an ordered dataset containing sequences of events represented by rows in a table, the task is to determine the minimum and maximum time intervals for consecutive rows that share the same event type. This problem arises when dealing with data involving gaps and islands, making traditional aggregation methods insufficient.

Understanding the Input

The input table consists of the following columns:

• name: Unique identifier for each person
• act: Event type, either "sleep" or "wake"
• rn: Row number within each person's sequence of events
• startt: Start time of the event
• endd: End time of the event

Identifying Consecutive Groups

To identify consecutive groups of rows with the same event type, we calculate the difference between the row numbers for the event type and the overall row numbering:

row_number() over (partition by name, act order by rn) as seqnum_na
row_number() over (partition by name order by rn) as seqnum_n

These new columns, seqnum_na and seqnum_n, represent the sequence number for the event type and the overall sequence number, respectively. Subtracting seqnum_na from seqnum_n creates a new column that represents the group number for each consecutive subset of rows within an event type.

Aggregation with Group Number

With the group number identified, we can aggregate the start and end times to find the minimum and maximum for each group:

select name, act, min(startt) as startt, max(endd) as endd
from (select i.*,
             row_number() over (partition by name, act order by rn) as seqnum_na,
             row_number() over (partition by name order by rn) as seqnum_n
      from input i
     ) i
group by (seqnum_n - seqnum_na), name, act;

By grouping by this group number along with the name and event type, we efficiently identify and aggregate the consecutive rows within each subset, delivering the desired minimum and maximum time intervals.

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