如何在Select语句中的SQL oracle中声明空列

Question

I'm trying to create a NULL column in the SELECT statement but it doesn't work:

SELECT mytable. *, NULL as ColumnName
FROM mytable;

The error code is

Error report -
SQL Error: ORA-01723: zero-length columns are not allowed
01723. 00000 -  "zero-length columns are not allowed"
*Cause:    Columns with zero length were not allowed.
*Action:   Correct the use of the column.

So it seems like it's not possible to do that. Is there any choice to create a NULL column in the SELECT statement?

Thank you,

Answer 1

You can cast() NULL to whatever type you want:

SELECT t.*, CAST(NULL as VARCHAR2(100)) as ColumnName
FROM mytable t;

Note: Your code should work just as a SELECT . The issue comes if you are trying to save the data.