Using Column Name returned by function in SELECT statement

Question

Hi
Output from my function (RETURN data type is VARCHAR2) is column name. I want to use it directly in my SELECT statement. Below is simplified example of this:
--- Function
CREATE OR REPLACE FUNCTION simple RETURN varchar2 IS
BEGIN
RETURN ‘my_column’;
END simple;
--- Select
SELECT simple FROM my_table;
This does not work. It seems that output from function is passed in quotation i.e.
SELECT ‘my_column’ FROM my_table;
So the output from SELECT is a list of rows populated with values my_table:
COLUMN     simple
ROW1     my_column
ROW2     my_column
ROW3     my_column
Can please someone help me with this?

Answer 1

I'm not sure I got you right.
In standard SQL everything must be known at compile time. If not dynamic SQL is required, but is a costly operation (usually requires parsing before each execution) so it should better not be used when standard SQL can do it.
I provided a design time example where a function returns the column name from the given the table name and column id for a varchar2 column data type to make things simple. Then a query string is constructed and executed dynymically to return all column values of the chosen table_name.column_name.
SELECT simple FROM my_tableAt compile time the simple function return value is unknown (any varchar2 value would do) you already find out you get the (same) return value (i.e column name) for each table row => dynamic SQL needed to get the column values
The purpose of function would be to rename all columns for provided table.The table name would be provided, right? If yes => dynamic SQL
What is the function supposed to return the column name (where would the new name come from?), the column alias (which table column would be renamed to the new name?)
The user could use the new_column name as the column alias name submitting the query.
Is it possible to do this?Maybe () using a pipelined function (different data types - number,date, ... not cosidered yet) but your simple query;
<tt>SELECT simple FROM my_table</tt>
might look like:
<tt>select my_column_value new_column_name from table(get_column_value(table_name,column_name))</tt>
Sorry, no Database at hand to provide a specific example.
Regards
Etbin