Gaps And Islands: Solving Stochastic Islands Problems

Kevin Feasel

2018-09-18

T-SQL

Itzik Ben-Gan shares with us a special case of the islands problem:

In your database you keep track of services your company supports in a table called CompanyServices, and each service normally reports about once a minute that it’s online in a table called EventLog. The following code creates these tables and populates them with small sets of sample data:

[…]

The special islands task is to identify the availability periods (serviced, starttime, endtime). One catch is that there’s no assurance that a service will report that it’s online exactly every minute; you’re supposed to tolerate an interval of up to, say, 66 seconds from the previous log entry and still consider it part of the same availability period (island). Beyond 66 seconds, the new log entry starts a new availability period. So, for the input sample data above, your solution is supposed to return the following result set (not necessarily in this order):

It’s a neat twist on an old problem.

Related Posts

Calculating Median In SQL Server 2019

Tomaz Kastrun shows that batch aggregation mode on window functions allow PERCENTILE_CONT finally to become useful: Next query, for median calculation was a window function query. SELECT DISTINCT PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY c1) OVER (PARTITION BY (SELECT 1)) AS MedianCont FROM t1 To my surprise, the performance was even worse, and at this time, […]

Read More

Generating SQL With Biml

Cathrine Wilhelmsen shows us you can do a lot more with Biml than just generating SSIS packages: This actually happened to me in a previous job. We had a fairly complex ETL solution for the most critical part of our Data Warehouse. Many SSIS packages, views, and stored procedures queried the tables that were replicas […]

Read More

Categories

September 2018
MTWTFSS
« Aug Oct »
 12
3456789
10111213141516
17181920212223
24252627282930