Zero/NULL Case Trick

In the book *Getting Started with SQL*, Thomas Nield talks about a technique he calls the ***zero/null case trick***: > There is a simple but powerful tool that can apply different filtering > conditions to different aggregations. We can create separate total > counts when a tornado was present versus not present in two separate > columns: > > SELECT year, month, > SUM(CASE WHEN tornado = 1 THEN precipitation ELSE 0 END) as tornado_precipitation, > SUM(CASE WHEN tornado = 0 THEN precipitation ELSE 0 END) as non_tornado_precipitation > FROM station_data > WHERE year >= 1990 > GROUP BY year, month > > What we have effectively done is get rid of the WHERE conditions when > tornado = 1 or tornado = 0, and then move those conditions to CASE > expressions inside the SUM() functions. If the condition is met, the > precipitation value is added to the sum. If not, a 0 is added, having > no effect. We do these for both columns, on for when a tornado was > present and one for when a tornado was not present respectively. > > You can make the CASE expression have as many condition/value pairs as > you need, giving you the ability to do highly particular interceptions > of values with your aggregations. You can also use this trick to > emulate crosstabs and pivot tables, expressing aggregations into > separate columns rather than in rows. A common example of this is > doing current year/previous year analysis, as you can express separate > years with different columns. ---------------- As a novice, that technique seems like it could come in really handy for summarizing data. I want to look up that technique online to get more information. The author of that book calls the technique the "zero/null case trick". But when I google that term, I don't get many results. Question: Is there a generally accepted name for that technique? (that would yield more results when searching online)