String comparison expression failing in Mapserver when including fieldname

Question

Within classes I'm able to match strings using CLASSITEM, but not when including the field name in the expression, for example (inside a layer declaration):

CLASSITEM "myfieldname"
CLASS
    EXPRESSION "sometext"
END

Works fine, but

CLASS
    EXPRESSION ([myfieldname] = "sometext")
END

Doesn't return any data

The second method is fine when working with integers, e.g.

CLASS
    EXPRESSION ([myintegerfieldname] = 10)
END

I've tried enclosing the strings with single quotes, double quotes, using a regex instead. The same behaviour occurs when the source data is a shapefile or a postgis layer.

Using CLASSITEM is obviously a good work-around, but it would be useful to know what I'm doing wrong with the direct comparison.

Thanks!

Answer 1

Try:

CLASS
   EXPRESSION ("[myfieldname]" = "sometext")
END

this should force mapserver to use the string equality operator on both fields and explains why it does work with numbers.