Why Are Empty Strings Treated as NULL in Oracle 9i's VARCHAR Columns?

Oracle 9i: Why Empty Strings Equal NULL in VARCHAR Columns

Oracle 9i's treatment of empty strings ('') as NULL values in VARCHAR columns is a historical artifact. Early Oracle versions designed VARCHAR and VARCHAR2 columns to interpret an empty string as equivalent to a NULL value. This stemmed from the idea that a missing value (empty string) is functionally identical to an unknown value (NULL).

The SQL standard subsequently defined a clear distinction between NULL and empty strings. This presented Oracle with a difficult choice: break existing applications by altering VARCHAR column behavior, violate the standard, or maintain backward compatibility at the expense of standard compliance.

Oracle prioritized backward compatibility, opting to maintain the existing behavior of VARCHAR. To address this incompatibility with the SQL standard, Oracle introduced VARCHAR2, a data type guaranteed to adhere to the standard's distinction between NULL and empty strings in later releases. Therefore, developers are strongly advised to use VARCHAR2 for new projects and to migrate existing code to avoid future compatibility issues.

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