How "Null" Selection works:

'Include Stars with No Value' column refers to unknown or blank values of the parameter for the star in the database. That is, the parameter value has not been entered for the star in the database.

The 'Include Stars with No Value' selection column has the following meaning:

• when selected and the range/limiting fields are blank, the archive will find those stars for which the particular quantities do not exist in the database.
• when selected and additional constraints have been specified in the range/limiting fields, the archive will retrieve all those stars for which either the parameter value matches the constraints specified OR those stars for which the parameter is undefined (ie has no entered value in the database).
• when unchecked, no action is taken regarding 'NULL' or 'blank' values of the parameter.