Performance: To use views or cursors, What is better??

We to are about to begin a second phase of development and of my part wanted opinions on the use of views or cursors, I do not compare complexity but performance

Agreed.
My assumption was that we were talking about the difference between
UPDATE some_table
SET some_column = (result of some view)and
FOR x IN some_cursor
LOOP
UPDATE some_table
SET some_column = x.<<something>>
WHERE some_other_column = x.key
END LOOP;If we're talking about returning data to a client application that is going to be doing row-by-row processing anyway, there is little or no difference.
Justin
Distributed Database Consulting, Inc.
http://www.ddbcinc.com/askDDBC

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TYPE r1 IS RECORD (
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<snip>
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<snip>
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> The reason I'm trying to use a REF CURSOR is that I was told that you
couldn't use CURSORs in Oracle Reports.
That does not change anything ito what happens on the Oracle server side. A cursor is a cursor is a cursor.
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> I'm trying to reduce the hits on the database from nested selects by
removing the dataset from the main SELECT statement and performing it only
once outside and then referencing this previously collected dataset inside the
main SELECT statement.
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a) identify the performance inhibitor issue correctly
b) address this issue correctly
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Hi sb,
I would say that it depends. You want your load to be efficient and your want your load to be simple and easy to enhance later. Sometimes these goals can be conflicting, so you need to decide what's important for your implementation.
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system.
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Query using views

Since the query is too big, I have removed the query from the post.
I would like to know whether using views in SQL queries degrade the performance of the queries?
When views are used in sql queries, the operation 'FILTER' is displayed in the explain plan, however the cost doesnt seem to be high. If the views can be replaced by the base tables, it is better to do so?
Edited by: user642116 on Nov 8, 2008 11:13 PM

user642116 wrote:
I have a main table called NATURAL_PERSON. There are several child tables based on this table, for e.g. PERSONAL_DETAILS, NATIONALITY_PERSON, CIVIL_STATUS etc. All these child tables have a foreign key NPN_ID which is joined with the ID of NATURAL_PERSON.
I need to obtain data from these child tables and present in them xmlformat.
A part of the query used is as below
SELECT npn.ID npn_id,
CONVERT(xmlelement("uwvb:NaturalPerson",
          XMLForest(LPAD(npn.nat_nummer,9,0) AS "uwvb:NatNr"),
          (XMLForest(LPAD(per.a_nummer, 10, 0) AS "uwvb:ANr"
          (SELECT XMLFOREST
                    (code_status AS "uwvb:ResidenceStatus")
                    FROM ebv_v_nep nep
                    WHERE npn_id = npn.ID
                    AND nep.nem_code = 'VBT'
                    AND nep.transactid =
                    (SELECT MAX (nep_i.transactid)
                         FROM ebv_v_nep nep_i
                         WHERE nep.npn_id = nep_i.npn_id
                         AND nep_i.nem_code = 'VBT'))
          entityelement),'WE8MSWIN1252', 'UTF8')
FROM ebv_v_npn npn, ebv_v_per per
WHERE npn.ID = per.npn_id
As seen in the above query, views have been defined for all the tables. For e.g. the view ebv_v_npn is based on NATURAL_PERSON, ebv_v_per is based on PERSONAL_DETAILS, ebv_v_nep is based on RESIDENCE STATUS. All these views are independent of each other and do not contain common tables in their definition.
The views can be replaced by the base tables as i dont see any advantage of using the views. I would like to know whether replacing the views with the base tables would also help to improve the performance.Replacing the views with the base tables might help, since not always Oracle is able to merge the views, so sometimes certain access paths are not available when working with views compared to accessing the base tables directly.
You can see this in the execution plan if there are separate lines called "VIEW". In this case a view wasn't merged.
The particular query that you've posted joins two views in the main query and (potentially) executes a scalar subquery that contains another correlated subquery for each row of the result set. "Potentially" due to the cunning "Filter optimization" feature of the Oracle runtime engine that basically attempts to cache the results of scalar subqueries to minimize the number of executions.
If the statement doesn't perform as expected you need to find out which of the two operations is the main contributor to the statement's runtime.
You can use DBMS_XPLAN.DISPLAY to find out what the FILTER operation you mentioned is actually performing (check the "Predicates Information" section below the plan output), and you can use SQL tracing to find out which row source generates how many rows. The following document explains how to enable SQL tracing and run the "tkprof" utility on the generated trace file: When your query takes too long ...
The correlated subquery of the scalar subquery that is used to determine the maximum "transactid" may be replaced with a version of the statement that uses an analytic function to avoid the second access to the view (note: untested):
SELECT npn.ID npn_id,
CONVERT(xmlelement("uwvb:NaturalPerson",
          XMLForest(LPAD(npn.nat_nummer,9,0) AS "uwvb:NatNr"),
          (XMLForest(LPAD(per.a_nummer, 10, 0) AS "uwvb:ANr"
          (SELECT XMLFOREST
    (code_status AS "uwvb:ResidenceStatus")
    FROM (
      SELECT code_status,
      RANK() over (PARTITION BY npn_id ORDER BY transactid desc) as rnk
      FROM ebv_v_nep nep
      WHERE nep.npn_id = npn.ID
      AND nep.nem_code = 'VBT'
    where rnk = 1)
    entityelement),'WE8MSWIN1252', 'UTF8')
FROM ebv_v_npn npn, ebv_v_per per
WHERE npn.ID = per.npn_idRegards,
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 Nov 10, 2008 9:27 AM
Added the rewrite suggestion

Performance: To use views or cursors, What is better??

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