How to return empty string in resultset (using sys_refcursor) in ORACLE DB

Question

After facing the problem:

ORA-32108: max column or parameter size not specified

I researched a little and I found these two questions: Why does Oracle 9i treat an empty string as NULL? and Oracle not distinguishing between nulls and empty strings? .

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These questions explain the error I get. But this led me to the next question - how can I return empty string as a field value in a ResultSet in Oracle?

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What I have so far is:

• create the statement
• register output parameter as oracle::occi::OCCICURSOR
• execute the statement
• the I call GetCursor to use the returned resultset

The execute fails, because of the error, described above.

So, how can I return such field in the resultset, which has value an empty string ('')?

In other words, I don't know how to apply the action, specified HERE - is it something server-side? Or I should add something in my code? Or in the stored procedure, that returns this resultset?

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I use OCCI (Oracle C++ Call Interface). My current workaround is to return a string, containing a single space (' '), but I don't like it.

Answer 1

If you want a completely NULL column returned you can use CAST(), which converts one data type into another.

For instance the following would generate a completely null column.

select a.*, cast(null as varchar2(1)) as null_column
  from my_table a

But, the database now understands that this should be a column of VARCHAR2(1), whereas if you use null as null_column there has been no maximum length specified.