Label Expressions to replace null values with text not in feature class

Question

I need to label some hydrants (points) - some of these belong to the fire brigade and have a number assigned to them, some do not and thus do not have a number. I would like to write an expression along the lines of:

'Label Hydrant with number if number exists, if hydrant has null value label with 'WO'.'

I just can't figure it out.

The simplest way for me to do this would be to change the null values to WO but the data is not mine, and I do not want to make changes to it. I suppose I could make a copy and put the values in the copy, but ideally I would like an expression.

Thanks!

Answer 1

You can use a simple script like this to label the features with Null values.

Function FindLabel ( [yourfield] )
  if isnull( [yourfield]) then
    FindLabel = "WO"
  else
    FindLabel = [yourfield]
  end if
End Function

Answer 2

Here is what you can do.

1. Set up two labeling classes under the labeling tab under the Method: Define clases of features and label each class differently.
2. Create a hydrant class that has numbers and one that does not (e.g. Number, & WO).
3. For the number class define the SQL Query as, "MyLabelField" <> ""
4. Point the number class to the correct label field.
5. For the WO class define the SQL Query as, "MyLabelField" = ""
6. For the WO class under the Expression option type, "WO"
7. Turn labeling on.

Answer 3

Further to @kenbuja sript which is the correct answer; If you have a combination of null and 0 length strings or spaces with no characters you could do something like this:

Function FindLabel ( [LABELFIELD] )
  if  isnull([LABELFIELD]) then
    FindLabel = "WO"
  elseif trim([LABELFIELD]) = "" then
    FindLabel = "WO"
  else
    FindLabel = ucase([LABELFIELD])
  end if
End Function