Keeping SQL Developer 4.0's Display Null Values during export

You can use the SQL*Plus set null command, which is one of many SQL Developer recognises.

When you set that and then run your query as a script (F5) the output appears in the Script Output window, and whatever text you specified appears instead of null. You can copy and paste from there but then you have to convert the text to data in Excel.

If you run your query as a statement (Ctrl-Enter) then the output in the Query Result window shows the value you set in the preferences, not what you specified with set null. However, when you right-click and export to CSV, the export file does use the set null string.

For example, if you set the null handling in your worksheet:

set null "NULL"

and then run a query as a script:

select 1 as id, null as value from dual;

the Script Output window shows:

        ID VALUE
---------- -----
         1 NULL 

If you run the query as a statement then the Query Result window shows the (null) from preferences rather then NULL:

But when you right-click and export as CSV, the file produced contains:

"ID","VALUE"
1,NULL

If you do set null "(null)" so that value matches the display preference then you won't notice the difference, of course.