Assume the data in the table is as following:
We can find out the value of type1 has D and null.
If I would like to find the data which Type1 is not eqal to D:
But Oracle return nothing
In Oracle, null represents a lack of data, a null cannot be equal or unequal to any value or to another null. Therefore, it will return nothing.
Hence, we can modify SQL statement as bellows:
The data which Type1 is null can be retrieved now: