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Identifies columns that contain (or do not contain) NULL field values. For example, on an uninitialized Boolean field, the value would be NULL rather than False of True. Similarly, for a numeric field, a NULL value would not be zero, but no numeric value at all.

Examples:

/* Extract all fields, where HireDate is NULL */

SELECT * FROM Employees WHERE (HireDate IS NULL);

 

/* Extract all fields, where HireDate is not NULL */

SELECT * FROM Employees WHERE (HireDate IS NOT NULL);