Hi,
I think you have found one of the things that the SQL syntax doesn't allow.
There is a few combinations that MapInfo doesn't allow. To get around them you
can most do your SQL in 2 steps in stead of just one:
1.
Select Sum(population) "SUM_POP", Sum(Area) "SUM_AREA"
From ...
Into SQL_PART1
2.
Select SUM_POP/SUM_AREA "Density"
From SQL_PART1
...
HTH,
Peter Horsb�ll M�ller
GIS Developer
Geographical Information & IT
COWI A/S
Odensevej 95
DK-5260 Odense S.
Denmark
Tel +45 6311 4900
Direct +45 6311 4908
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Fax +45 6311 4949
E-mail [EMAIL PROTECTED]
http://www.cowi.dk/gis
-----Original Message-----
From: Lawson Key [mailto:[EMAIL PROTECTED]
Sent: Friday, December 10, 2004 5:54 PM
To: [EMAIL PROTECTED]
Subject: MI-L Defining a custom field in an SQL Select Query - Making
expressions with Functions
Hi list,
I'm doing some population density calculations using the SQL Select tool. I
have population data and area data for several hundred regions in a table. In
order to get the aggregate density for the total area, I'm summing these two
fields in a query and manually dividing total population by total area. My
issue is that MapInfo allows me to define two separate columns using the sum(*)
function, but when I try to define a single density field, which looks
something like this:
Sum(population)/Sum(Area) "Density"
It doesn't work. "Found[/] while searching for [A string constant]" is the
error I get. Interestingly, the following custom fields do work:
Population/Area - returns the density of each region in the table
Sum(Population/Area) - returns the sum of all regions' density, which is
meaningless.
I don't want a MapBasic solution, I would just like someone to confirm that
what I'm trying to do is not allowed, or let me know if there is a way. This
problem isn't keeping me from doing my work, I'm just surprised that this
functionality isn't available and want to test my findings with the list.
Using MapInfo Pro 6.5
Lawson Key
CenturyTel
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