Problem: Querying for NULL values in a shapefile or coverage crashes ArcMap
Using the following SQL statement in the Select By Attribute dialog to query blank records in a shapefile or coverage will cause ArcMap to crash:
Using an operator (=, -, *, /) will prevent the crash, but no records will be returned.
This is a known issue.
Solution or Workaround
This problem is addressed in ArcGIS 8.1 Service Pack 1. See Related Information section to download this pack.
For all versions of ArcGIS, use two single quotes to query for blank values in a string field and a zero to query for blank records in a number field. For example:
"StringField" = ''
"NumberField" = 0
Shapefile and Coverage attribute tables are not capable of storing NULL values in number and string fields, only NULL dates are permitted. ArcGIS does not recognize NULL date values.