Histogram Query

Access Histogram query example - you'll be surprised at how easy it is to do the calculations for a seemingly complex statistical measure using a single Access query.  In this example we have customers who purchased items from a store.
We want to know the distribution of customer purchases grouped by customer's age.   To start, we have a table called M_Customer_Purchases (in reality this would probably be a query based on a Customer table and a Purchases table).

The table has 2 fields (the purchase_date field is really not required for this example). 

Age
Purchase_Date

The following sql statement will group the ages (purchases) into 6 categories based on the customer's age.  You can see the bracketing of the age in the immediate if statement (iif) - this created the Access histogram values.

SELECT
Sum(IIf([Age]<18,1,0)) AS Group1,
Sum(IIf([Age]>=18 and [Age]<30,1,0)) AS Group2,
Sum(IIf([Age]>=30 and [Age]<40,1,0)) AS Group3,
Sum(IIf([Age]>=40 and [Age]<50,1,0)) AS Group4,
Sum(IIf([Age]>=50 and [Age]<60,1,0)) AS Group5,
Sum(IIf([Age]>=60,1,0)) AS Group6
FROM M_Customer_Purchases;

The following is the result of the Access example query.  You could easy pass this query to a bar chart to display the results graphically.

Note the trick is the 1, 0 in the iif statement - when the age matches the age range in the iif statement then the result is one, otherwise the result is 0, thereby providing a way to SUM the results. 

You should be able to see how you can bracket results for all kinds of data.  You could bracket date ranges to simulate a crosstab query (pivot query).  One advantage of using the method in this example over crosstabs is that you can pass query parameters to the query from a form field.

You can combine this query technique for histogram calculations with our bar chart example.  The code in the bar chart example will work with forms or reports. 

Go to our download center to download and run the Access Bar Chart/Bar Graph example.