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In Oracle SQL, a blank space is considered a valid value and can be included in a case statement. However, including a blank space as a specific case value can lead to unexpected results or errors if it is not handled properly. This is because a blank space is seen as a unique value rather than a null value, and it may be treated differently by comparison operators or functions.

For example, if you have a case statement that includes a condition for " ", and your data contains both blank spaces and null values, the query may return unexpected results or errors. To avoid this issue, it is recommended to handle null values separately and use the NULL keyword instead of a blank space if necessary.