null vs empty string in Oracle [duplicate]

Answer 1

In oracle an empty varchar2 and null are treated the same, and your observations show that.

when you write:

select * from table where a = '';

its the same as writing

select * from table where a = null;

and not a is null

which will never equate to true, so never return a row. same on the insert, a NOT NULL means you cant insert a null or an empty string (which is treated as a null)

Answer 2

This is because Oracle internally changes empty string to NULL values. Oracle simply won't let insert an empty string.

On the other hand, SQL Server would let you do what you are trying to achieve.

There are 2 workarounds here:

1. Use another column that states whether the 'description' field is valid or not
2. Use some dummy value for the 'description' field where you want it to store empty string. (i.e. set the field to be 'stackoverflowrocks' assuming your real data will never encounter such a description value)

Both are, of course, stupid workarounds :)