I have an internet map server connected to my database. Until now,
"no data" fields within the table were filled with a "-9999", i.e.
"-9999" equalled "no data available".
Now, for displaying a map with different classes (red for values from
0-100, green for values from 100-200....) I need to build as well a
class for "no data" (which is displayed in grey). Until now that
worked perfectly well with the "-9999" values. But since I inserted a
couple of new countries (which do not find any corresponding values
in the tables, as they don't yet exist), I receive the usual "-9999"
plus "NULL" values. Both should be considered as "no data" and thus
displayed in grey.
Unfortunately the mapserver can't deal with NULL values. So, I can't
build a class saying
if values = NULL do something
but instead it only works with "fake" NULL values as -9999
if values = -9999 do something
Stef
Aside from your database structure being problematic, what are you
trying to accomplish?
In other words, what do you want to replace the nulls with and in
what circumstance?
I imagine your table looks like this
ID,country,1950,1951,1952,1953,....
1 usa 50 null 70 10
2 canada 10 45 null 4
Please mention what you would like to do with this?
Stefan Schwarzer wrote:
On Thu, Sep 07, 2006 at 07:45:19AM +0200, Stefan Schwarzer wrote:
Hi there,
is there a simple way to replace NULL values in multiple columns
within the SQL statement? I changed the underlaying country
template
of your database; so now there are a couple of NULL values when I
join the stats-table with the country table. Unfortunately, my
queries have always multiple (year) columns, so I can't do a
kind of
manual replace.
I found that the COALESCE command does something like this, but I
couldn't figure out how this works.
Yes, COALESCE replaces NULLs, however your examples have neither
NULLs
nor use COALESCE, so I don't understand what your question is.
Please repost with an actual example of your problem.
As I said, I couldn't figure out how COALESCE would work on
multiple columns (without naming them explicitly).
So, say I have a table with columns for each year between 1970 and
2005. For specific countries the values might be NULL, depending
if the statistical table has been updated recently (then they will
have a value), or not (then they will be NULL). A sample query
would thus be something like:
SELECT * FROM pop_density
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