dbnull ( numeric_expression )
dbnull ( database_number , numeric_expression )
dbnull ( database_number , database_recordset_number , numeric_expression )
dbnull ( string_expression )
dbnull ( database_number , string_expression )
dbnull ( database_number , database_recordset_number , string_expression )

returns boolean_expression

Return a true if the specified column number or name of the current row of the open recordset is a NULL vale. If the field contains a value a false will be returned.

See example of usage on DBOpen page.

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