Ref cursors for stored procedure

Question

Hi every body,
I am new one,I am in learning stage.
My java developer was ask me give set of results.
i am using in my code sys_refcursor, my questions are.
SQL> create or replace procedure sysref(p_out out sys_refcursor) is
2 begin
3 open p_out for select empno,ename from employee;
4 end;
5 /
I am using the procedure like above procedure.
1) How to use ref cursors in procedure. what is the main use.
2) How to close ref cursors in procedure.If it is need.
3) How to use exceptions in procedures for ref cursors.
Give me one example with complete structure.
Please help me
new one
Edited by: subba on Aug 19, 2010 12:08 AM
Edited by: subba on Aug 19, 2010 12:09 AM

Answer 1

subba wrote:
1) How to use ref cursors in procedure. what is the main use.All SQL in Oracle are parsed as cursors in the Shared Pool. The client code (be that PL/SQL or Visual Basic or Java) gets a handle or reference to this SQL cursor on the server.
Using this handle, the client can fetch rows using the cursor (the cursor is like a program - the executable binary version of the source SQL code).
Clients implement their interfaces with this SQL cursor handle in different ways. PL/SQL alone supports:
- implicit cursor handles
- explicit cursor handles
- DBMS_SQL cursor handles
- reference cursor handles
Why so many? Different tools for different jobs. Each has its pros and cons and each is suited for specific (and different) types of problems.
A ref cursor is special in that PL/SQL can pass this SQL cursor reference handle to an external client to use - like Java.
Why?
The basic concept is that of abstraction. Removing the complexities of SQL and the database design and SQL optimisation from the Java code. Instead, Java calls a PL/SQL proc. This proc creates the SQL cursor, and uses a reference cursor variable to store the SQL cursor handle. It can then pass this to Java. This means that the entire SQL is encapsulated in the PL/SQL proc. We can now modify it, optimise it, support data models changes in the database via the PL/SQL proc... all without even having to recompile the Java code that makes the call and consumes the ref cursor the PL/SQL proc gives it.
2) How to close ref cursors in procedure.If it is need.Yes. A very important factor - well spotted.
As PL/SQL can pass ref cursors to external clients. it does not automatically close these cursors. It does not know when the client has consumed the cursor. It will only close it when the cursor is still open, when the Oracle server session is terminated.
So it is important that the client (Java in this case) closes the cursor when done. If not, the cursor will remain open, will continue to occupy server resources... and if the client opens more and more of these cursors, the server process will run out of resources.
Cursor leakage by Java developers are common - and can simply be avoided by closing the cursor once the Java code has consumed it.
3) How to use exceptions in procedures for ref cursors.No. Why? Why would you want to deal with the exception in a PL/SQL proc? The Java code wants to open that cursor. It knows why. It knows what to do when that cursor fails or is empty. It interacts with the user. How is the PL./SQL proc, whose only function is to construct the SQL and pass the cursor handle to Java, to know any of this?
Exceptions in this regard should typically be handled in Java. Not in PL/SQL.
Of course, if that PL/SQL proc has parameters, it also needs to validate these and it needs to raise application exceptions to inform the Java caller when these parameters are invalid.
But actually catching exception in this case... does not make much sense. As what can the PL/SQL do about the error when it is a "server" and Java is the "client"?
It is like saying that the Oracle Server should handle all exceptions when TOAD is used and incorrect SQL is passed to it. How does it make sense for Oracle to process SQL errors and the TOAD client not getting any results from a wrong SQL and not knowing that there was even an error with that SQL?