4 replies to this topic

[tellett]

Hello all, I have a problem selecting null values in ArcMap.

Essentially, what I am trying to do is compare an updated dataset with the original.
The way I am doing this is too join the two tables and then simply select the rows
where there are null values (which is what arc puts in fields when rows cannot be
matched). The value in the fields is actually <NULL>, but I assume thats the same
as null. So my query is:

SELECT * from Table where Field IS NULL

But its not selecting the row. I am most confused and frustrated!!

Thanks in advance for the answer!!!!

[Matthew Hampton]

I copied this from 9.2-Help.


"The NULL keyword
You can use the NULL keyword to select features and records that have null values for the specified field. The NULL keyword is always preceded by IS or IS NOT.

For example, to find cities whose 1996 population has not been entered, you can use

"POPULATION96" IS NULL"

[ELeFevre]

This might provide a little insight into your problem. "How can I select only the null values on a joined table?"

[tellett]

Thanks for your help everybody, but none of it seems to work unfortunately.
What I've done is do 'is not null', which selects all the records I don't want,
and then simply invert the selection. A quick run around in the face of
overwhelming illogic!!!

[David T]

Well, <Null>, if that's what is actually in the field (as opposed to no information in the field), is a text string. So you would need to select for '<Null>'.