All data types in the Oracle database implement the null value. Null is a very special value which means ‘Unknown’. That means that the value is really unknown. Null is not equal to null, because both are not known. Therefore you cannot compare them to each other.

Even the boolean value has this null value implemented. Where you should expect a boolean value to hold either true or false, in Oracle a boolean value can also hold null as a value. So a boolean value has three possibilities instead of the two you normally expect.

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