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The IS NULL extended comparison operator indicates if a field contains a NULL value. The syntax is:
Field_reference IS [NOT] NULL
Use the IS NULL extended comparison operator to filter a table based on the specified field containing a NULL (empty) value. The following example returns all Customers where the BankReference field is null:
SELECT * FROM ARCUST WHERE BankReference IS NULL
Use IS NOT NULL to return the converse of a IS NULL comparison. For a numeric field, a zero value is not the same as a NULL value.
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