Looping over cursor returned from procedure with many tables - sql

Question

I'm working with a stored procedure that I didn't write, which is long and contains numerous columns and joins. The procedure returns a cursor, which the application server (.NET, incidentally) picks up and iterates through.
I'm trying to intercept the cursor using SQLPlus and PL/SQL but I'm having a hard time trying to figure out how to set up the script. Here's what I have so far:
DECLARE
cur sys_refcursor;
BEGIN
adv_schema.report_proc('CAL','01-JAN-2011','01-JAN-2012','Y',cur);
OPEN cur FOR --??????
LOOP
FETCH cur INTO column1, column2;
EXIT WHEN cur%NOTFOUND;
DBMS_OUTPUT.Put_Line ('First Name: '||column1||' Last Name: '||column2);
END LOOP;
END;
/
What do I put in the OPEN statement? All the examples I've seen of how to do this are overly simplified examples where some table 't' is created right there in the PL/SQL block, then a cursor is opened with a query to that table, to loop over. What about when a procedure returns a cursor to a complex query with multiple tables?

Answer 1

Assuming that the report_proc procedure is returning the cursor (i.e. the fourth parameter is defined as an OUT SYS_REFCURSOR), there is no need to OPEN the cursor in your code. The procedure is already opening it. You just need to fetch from it.

Answer 2

As #Justin has already mentioned, there is no need to open the cursor returned by the report_proc procedure, you only need to fetch from that cursor. Ref cursors are weak cursors(basically cursors that return no type) and in order to fetch from a weakly typed cursor, you need to know what to fetch. When you know what type a cursor returns you can declare a local structure to fetch into, like so:
DECLARE
-- example of record
-- in your case you have to know exactly
-- how many column and of which datatype your ref cursor returns
type T_Record is record(
column_1 number,
column_2 number
);
l_record T_Record;
cur sys_refcursor;
BEGIN
adv_schema.report_proc('CAL','01-JAN-2011','01-JAN-2012','Y',cur);
LOOP
FETCH cur
INTO l_record;
EXIT WHEN cur%NOTFOUND;
DBMS_OUTPUT.Put_Line ('First Name: '||l_record.column1
||' Last Name: '||l_record.column2);
END LOOP;
END;
Also, if you simply need to print the content of a ref cursor, you can do it in SQL*Plus as follows:
SQL> variable cur refcursor;
SQL> exec adv_schema.report_proc('CAL','01-JAN-2011','01-JAN-2012','Y', :cur);
And then use print command to print the refcursor cur:
SQL> print cur;
Do I need to fetch every column that the cursor returns, or can I fetch a subset, say the first three.
No, you fetch everything, you cannot be selective in what column to fetch. It's not impossible however, but it will involve using dbms_sql package, specifically dbms_sql.describe_columns procedure to get information about columns for a cursor.
Just for consideration, If you know that a specific column is definitely present in a cursor, you could use xmlsequence() function to fetch a specific column specifying its name in the extract() function:
SQL> declare
2 type T_List is table of varchar2(123);
3 l_names T_List;
4 l_ref_cur sys_refcursor;
5
6 begin
7 open l_ref_cur
8 for select first_name, last_name
9 from employees
10 where rownum <= 5;
11
12 SELECT t.extract('ROW/FIRST_NAME/text()').getstringval()
13 bulk collect into l_names
14 FROM table(xmlsequence(l_ref_cur)) t;
15
16 for indx in l_names.first..l_names.last
17 loop
18 dbms_output.put_line(l_names(indx));
19 end loop;
20 end;
21 /
Result:
Ellen
Sundar
Mozhe
David
Hermann
PL/SQL procedure successfully completed