If I wanted to select everything but NULL, I would have used this SQL expression. The records with NULL in the TFIELD are selected. Using the Select By Attributes tool, I can select NULL values in the TFIELD by constructing the following SQL expression. Note some records have NULL values while others have data. So let’s take a look at some test data I created with some fields that allow NULLs.Īs you can probably guess, the field TFIELD is a text field and NFIELD is a numeric field. Also, keep in mind that you can add a field with “Allow NULL Values” set to “No” only if your feature class or table is not populated yet with records.

If you set it to “No” and do not specify a “Default Value”, then Text fields will default to a blank (empty) value and numeric fields will default to zero. If you do not want NULLs, set it to “No”. Note by default in the Field Properties that “Allow NULL Values” is set to “Yes”. Then open the data’s attribute table and select “Add Field…” from the Table Options icon. So how do you specify a field to allow NULLs or not? Open ArcMap (I’m using version 10.2.2) and bring in some data from a geodatabase.

More than likely you have fields that allow NULLs because someone created them not paying attention to the defaults. You could use a NULL value to represent “not known”, since zero is a valid elevation. Another example would be an elevation field. A good example would be an employee database with a termination date field that is set to NULL when the employee is new. Why have a NULL value in your data? Usually this is used to mean “not set” or “uninitialized”. And yes, you can have NULLs in numeric fields too! Allowing a field to be NULL introduces an additional state that you would not have if the field was created to not allow NULLs.

A NULL value is not the same as a blank (empty) value, and actually takes up 1 bit more of space than an empty value. NULL values in GIS data can trip you up if you don’t know how to deal with them.

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