Hi, from your screenshot I would guess that there is already a field named DEVS_D present, here's why: In the expression field you have to enter the VALUE you want to be calculated for the field, so if for example you want to create a new field named DEVS_D and assign the value 1 to all rows, then you have to simply type: 1 (and not DEVS_D = 1). By entering DEVS_D = 1, the expression "DEVS_D=1" is evaluated and a true/false value is returned, ie for rows that the EXISTING field DEVS_D is 1 you will get a 1 while for those that DEVS_D is not 1 you will get a 0. Now, if there is no field named DEVS_D, then the expression would not validate and on the preview you would get a "Expression is invalid" and OK would be grayed out.
If this is indeed the case, then I would classify it as a bug, since insufficient information is returned regarding the cause of failure. Regards, Stefanos -- Sent from: http://osgeo-org.1560.x6.nabble.com/QGIS-User-f4125267.html _______________________________________________ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user