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Summary queries (also called Group-By queries) are used to summarise the contents of a table.
There is an important rule about summary queries which you need to be aware of. All columns in the group-by query need to be either:
This is best illustrated with an example. The following query summarises customer revenue by customer and month:
Select customer_code, month, sum(revenue) from orders group by customer_code, month
In this:
The columns you are summarising by are specified as Group-By columns. In the Query-Column Grid you select these by clicking on the Group-By column.
The columns you are summarising must have a summary function. This indicates how you are summarising the column. In the above example, the summary function is sum(). Other functions are: min(), max(), avg(). These can be seen in the Functions drop-down list.
So, the rule for a summary query is that all columns must have either:
When you are doing a summary query you can also specify a Having clause to select the summary rows for your result-set.