3. QUEL Data Types : Nulls
 
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Nulls
A null represents an undefined or unknown value and is specified by the keyword null. A null is not the same as a zero, a blank, or an empty string. You can assign a null to any nullable column when no other value is specifically assigned. For more information about defining nullable columns, see Create Statement—Create a Table.
The ifnull function and the is null predicate enable you to handle nulls in queries. For details, see Ifnull and Is Null Comparison.