Howto replace Permanent "Temp" table?

Question

Hi,
I'm joining a project, but I am too novice on PL/SQL. One particular Procedure does a search query. The approach can be summarized as:
* Build a SQL string base on values passed in the list of parameters
* Truncate a permanent table named Temp_SearchID
* Execute the dynamic SQL string which will populate the Temp_SearchID table (INSERT INTO Temp_SearchID SELECT ...)
* Populate the returned cursor by a SELECT joining other tables with the IDs in Temp_SearchID
{color:#ff0000}*Q1.*{color} If the application load increases, there will be a higher concurrency and let assume that there are several simultaneous calls to the procedure above. What would happen as all these calls has different parameters and they all want to compete to use the Temp_SearchID table their own way?
*{color:#ff0000}Q2.{color}* If the approach using a permanent Temp_SearchID table is not recommended, it is possible to dump the IDs in a cursor which is local only to the procedure. Then make a SELECT joining with this cursor? In the SQL Server world, this is possible using Table variable or session local temp tables. If it is possible to achieve this with PL/SQL, can you please show me the syntax or point me to some code snippets?
Thank you very much for any help.

Answer 1

CarbonFiber wrote:
In the scenario I am dealing with, the business rules are a little bit complex. Writing the entire SQL query in a string would indeed solve the problem. But it would be come hard to debug & test as the entire query now appear as a big string. I might ressort to that. As I am used to SQL Server, I would like to know if Oracle has a memory based structure, then join it with other tables to produce the final results. I don't know PL/SQL well enough to write a query joining a cursor with a table. Can you show me the PL/SQL syntax to do that?
From a performance perspective in Oracle the single, plain SQL approach probably would be the best, depending on some other factors, like e.g. how sharable the SQL generated would then be (or are you going to generate then literally thousands of different large SQL statement as part of your process).
As already discussed here you have in Oracle the option to create a GLOBAL TEMPORARY TABLE that holds data visible only to the session that's using it, but it's still writing/reading that data potentially from disk.
The subquery factoring approach outlined by David might also be a quite good option if statement complexity is your main issue.
The in-memory approach in Oracle is a bit more complex. You would need to create an type, a collection type on top of that and then use the PL/SQL collection to use in the query, e.g. like that:
create or replace type t_qualified_id as object (
productid integer
create or replace type t_qualified_id_array as table of t_qualified_id;
create or replace procedure test_collection as
  in_memory_table t_qualified_id_array;
begin
  select t_qualified_id(object_id)
  bulk collect into in_memory_table
  from user_objects;
  for rec in (select object_id
  from table(in_memory_table) a
  inner join user_objects b
  on a.productid = b.object_id) loop
    null;
  end loop;
end;
/or like that if you don't want to use the "object" type, you can just create an array of the built-in number/integer type.
create or replace type t_qualified_id_array as table of integer;
create or replace procedure test_collection as
  in_memory_table t_qualified_id_array;
begin
  select object_id
  bulk collect into in_memory_table
  from user_objects;
  for rec in (select object_id
  from table(in_memory_table) a
  inner join user_objects b
  on value(a) = b.object_id) loop
    null;
  end loop;
end;
/But you can see that there are subtle differences and you need to study the SQL and PL/SQL developer guide to get the details. It gets even more confusing because you can have in Oracle PL/SQL collection types and SQL collection types which differ in various aspects in terms of usage.
Regards,
Randolf
Oracle related stuff blog:
http://oracle-randolf.blogspot.com/
SQLTools++ for Oracle (Open source Oracle GUI for Windows):
http://www.sqltools-plusplus.org:7676/
http://sourceforge.net/projects/sqlt-pp/
Edited by: Randolf Geist on Sep 22, 2008 6:57 PM
Subquery factoring mentioned