A derived column is a column in a query table whose contents are created by applying an expression to the values of columns already existing in some base table. In the example above, population density was a derived column. By default, the Select Columns box contains an asterisk (*), indicating that all of the columns in the base table are to be included in the query table. If you do not want all of those columns, you should delete the asterisk and list only those columns that you want to use. You are not limited to creating one derived column. You can create as many derived columns as you want. Note that the more derived columns you create, the longer it will take MapInfo Pro to execute the query.
You can also create derived columns based on the aggregate functions count, sum, avg, wtavg, max, and min. For example:
- sum(Population)
would give you the population for the entire world.
- sum(Area(obj), "sq mi")
would give you the area for the entire world.