Newbie Trouble Figuring Out Compile Error in Procedure

Question

I'm inexperienced at PL/SQL programming and I've been reading through the 10gR2 PL/SQL user's guide trying to figure out what's wrong with my procedure but I'm not having any luck. I would appreciate your help.
I wanted a procedure that I could use on small tables (which are not partitioned by date) that I could use to delete rows older than days_old days old. I wanted it to be generic so I didn't want to have to hard code the table name (table_name), table's primary key (primary_key) or the name of the column in table_name that I wanted to match dates against. Here's what I came up with:
CREATE OR REPLACE PROCEDURE delete_old_rows (table_name VARCHAR2, primary_key VARCHAR2, date_col_name VARCHAR2, days_old NUMBER) AS
v_sql VARCHAR2(256);
CURSOR rows_to_delete IS
SELECT primary_key FROM table_name WHERE date_col_name < trunc(SYSDATE) - days_old;
BEGIN
FOR del_rows in rows_to_delete
LOOP
SELECT 'DELETE FROM table_name WHERE date_col_name = del_rows.date_col_name' INTO v_sql FROM dual;
DBMS_OUTPUT.PUT_LINE(v_sql);
-- EXECUTE IMMEDIATE v_sql;
END LOOP;
END;
SHOW ERRORS;
The compiler seems to be okay with my use of primary_key, date_col_name, and days_old as variables but when I start using the table_name variable I get a "SQL Statement Ignored" error on the SELECT in the CURSOR and a "table or view does not exist" error on the same statement.
So, it compiles okay without using the table_name variable but it does no compile okay when I start using it.
And yes, I know the EXECUTE IMMEDIATE is commented out -- I'm still developing it.
Thank you

Answer 1

Currently your cursor is referring to a table called "table_name" with a column called "date_col_name". To build a dynamic cursor using the table_name etc parameter values you are going to need dynamic sql, e.g:
OPEN c_rows_to_delete FOR
    'SELECT primary_key FROM ' || table_name || ' WHERE ' || date_col_name || ' < trunc(SYSDATE)';where c_rows_to_delete is declared as a SYS_REFCURSOR. You can't use a Cursor FOR loop on ref cursors.
Also PL/SQL has a handy assignment operator ":=" so you don't need to SELECT INTO FROM DUAL.
Generally dynamic code is something to be used as a last resort.