If you ever have to start working with Oracle you have to keep in mind that NULLs and blank values don't work exactly the same as in SQL Server. Let's take a look at some examples

Create this table and insert some rows

As you can see we inserted four rows, one row is null, one row is blank, one row has a space and one row has Bla.

Now let's run the following query

Here are the results in a html table

Here is an image of the same results

See what happened, Oracle changed the blanks to NULLs.

We can easily test this theory, let's create a table with a column that has a not null constraint

Now of course if you try to insert a NULL it will blow up

Here is the error
SQL Error: ORA-01400: cannot insert NULL into ("SYSTEM"."TESTNULL2"."COL2")
01400. 00000 - "cannot insert NULL into (%s)"

Inserting Bla works without a problem

What about a blank, what will happen now?

SQL Error: ORA-01400: cannot insert NULL into ("SYSTEM"."TESTNULL2"."COL2")
01400. 00000 - "cannot insert NULL into (%s)"

As you can see the blank gets converted to a NULL and you get the same error. This is very different from SQL Server.

Will a space succeed?

A space is no problem.

Coalesce differences
Just be aware that coalesce won't work the same either. Oracle doesn't have isnull but it has the nvl function instead

Run the following two statements

In both cases you are getting No back from the function, as you can see a blank is treated as null.

Be aware of these differences between Oracle and SQL Server, you could have some strange results back from queries if you assume it works the same

We will take a look at that strange table dual in another post