Gaps And Islands: Call Center Edition

Kevin Feasel

2017-02-22

T-SQL

Kathy Kellenberger solves an issue with tracking contiguous calls within a call center:

To come up with a solution, I first thought about how to solve it with a traditional cursor. I won’t provide a cursor solution here, but it would involve looping through the rows in order and finding the first and last employee rows. When the last EmpID doesn’t match the next EmpID, then the previous row is the last call for the previous EmpID and the current row is the first call for the next EmpID.

NOTE: The solution to this problem assumes that there are at least two calls per shift.

In 2012, four T-SQL window functions became available that let you look at expressions from different rows: LAG, LEAD, FIRST_VALUE, and LAST_VALUE. For this puzzle, LAG and LEAD seemed to be the answer.  In this case, I used the optional default parameter to replace any NULLs with -1.

This is a particular solution for the Gaps and Islands problem; here’s Itzik Ben-Gan on the topic.

Related Posts

Pitfalls with Window Functions

Itzik Ben-Gan takes us through two issues you might run into when using window functions: There are two common pitfalls involving window functions, both of which are the result of counterintuitive implicit defaults that are imposed by the SQL standard. One pitfall has to do with calculations of running totals where you get a window […]

Read More

Spaces in CHAR Columns

John McCormack wants to store a single space in a CHAR(1) column: I was asked by a colleague why his where clause wasn’t being selective when filtering on a space value. The column was a char(1) data type. To understand the curious case of the space in char(1), we need to understand how the char […]

Read More

Categories

February 2017
MTWTFSS
« Jan Mar »
 12345
6789101112
13141516171819
20212223242526
2728