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Understanding the IS operator and how to work with NULL values is an integral part of SQL programming. SQL treats “NULL” as a special value that represents missing or unknown data. This is somewhat different from the way most programming languages handle null values, making it a crucial concept for new and intermediate SQL users.
One common use of the IS operator is in comparison scenarios involving NULL values. When comparing a NULL value with another value using a typical comparison operator (=, <, >, etc.), the result will always be NULL or unknown. This is where the power of the ‘IS’ operator comes into play.
Understanding the IS Operator
The IS operator in SQL is used to compare a value with NULL. It is used in the WHERE clause of SELECT, UPDATE, and DELETE statements. In SQL, the syntax is very straightforward:
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column_name IS NULL column_name IS NOT NULL |
The expressions return true if a column value is NULL or not NULL, respectively.
Examples
Selecting NULL values
To select data that includes NULL values from a database, use the IS NULL operator. For example:
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SELECT EmployeeId, LastName, FirstName FROM Employees WHERE OfficeCode IS NULL; |
This will return all employees who do not have an office code set.
Selecting non-NULL values
The IS NOT NULL operator is useful when you want to retrieve records that do have a particular value. For example:
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SELECT EmployeeId, LastName, FirstName FROM Employees WHERE OfficeCode IS NOT NULL; |
This will return all employees who do have an office code set.
Conclusion
The IS operator is very powerful in SQL for dealing with NULL values. Not only does it allow you to find records with NULL and non-NULL values, but it allows you better control over your data in general. By understanding how to use the IS operator effectively, you can ensure you’re taking full advantage of what SQL has to offer.