Once again Martijn is correct, and you have to use "is null" not "=null"
One thing you might want to consider is adding -9999 as a default value
in the table so that when new data is entered it with a null it
automatically gets the correct value.
Using coalesce with the value will probably be the simplest for you.
Try select ...,coalesce(datafield,-9999) as datafield,... and that will
change all nulls to -9999 and give it the correct fieldname.
Stefan Schwarzer wrote:
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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