Calculating filtered aggregates

If we want to count the number of occurrences of an event given some filter criteria, we can take advantage of aggregate functions like SUM(), MIN(), and MAX(), as well as CASE expressions. For example, MAX(CASE WHEN ir.IncidentTypeID = 1 THEN ir.IncidentDate ELSE NULL END) will return the latest incident date associated with incident type 1. If you include one MAX() statement for each incident type, you have pivoted the data set by incident type ID.

In this scenario, management would like us to tell them, by incident type, how many "big-incident" days we have had versus "small-incident" days. Management defines a big-incident day as having more than 5 occurrences of the same incident type on the same day, and a small-incident day has between 1 and 5.

Fill in a CASE expression which lets us use the SUM() function to calculate the number of big-incident and small-incident days.
In the CASE expression, you should return 1 if the appropriate filter criterion is met and 0 otherwise.
Be sure to specify the alias when referencing a column, like ir.IncidentDate or it.IncidentType!

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Exercise

Calculating filtered aggregates

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