Category: SQL | PLSQL

Database, Java | DevOps | APEX | Scripts, SQL | PLSQL

Oracle SQL: Aggregate List – LISTAGG

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Know this command?

I think it’s very useful, but not so often I see that in use… More about it:

It was introduced in Oracle 11g Release 2, as an analytic function to make the life easier fot the PLSQL Dev, specially when working to aggregate strings. The nice thing about this function is it also allows us to order the elements in the concatenated list. If you are using 11g Release 2 you should use this function for string aggregation.

In case WM_CONCAT is in use for this end, be aware that WM_CONCAT is an undocumented function and as such is not supported by Oracle for user applications (MOS Note ID 1336219.1). Also, WM_CONCAT has been removed from 12c onward, once it was completely replaced by LISTAGG.

More info and examples can be found here: https://oracle-base.com/articles/12c/listagg-function-enhancements-12cr2

Hope you enjoy it. Cheers!

Database, SQL | PLSQL, Tools

PLSQL: Which code is taking longer?

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So you have a slow process calling several PLSQL Codes, including Procedures, Functions and etc, but don’t know what is taking longer?

Your problems has ended… 

In Oracle 11gR1 was introduced the PL/SQL Hierarchical Profiler to help developers by providing hierarchical profiler data analysis for PL/SQL programs.

From Oracle base:
“The hierarchical profiler consists of the DBMS_HPROF package, which feels similar to the DBMS_PROFILER and DBMS_TRACE packages, and the plshprof command line utility to converts the profile information into HTML format.”

For example, we can set a profiler for procedure proc_example_1 and check in all calls and related statistics:

BEGIN
  DBMS_HPROF.start_profiling (
    location => 'ORACLE_DIR',
    filename => 'prof.txt');

  proc_example_1(p_number => 10);

  DBMS_HPROF.stop_profiling;
END;
/

And to see results, a simple output is:

COLUMN owner FORMAT A20
COLUMN module FORMAT A20
COLUMN type FORMAT A20
COLUMN function FORMAT A25
SELECT symbolid,
       owner,
       module,
       type,
       function
FROM   dbmshp_function_info
WHERE  runid = 1
ORDER BY symbolid;

  SYMBOLID OWNER                MODULE               TYPE                 FUNCTION
---------- -------------------- -------------------- -------------------- -------------------------
         1 TEST                 proc_example_1       PROCEDURE            proc_example_1
         2 TEST                 proc_example_2       PROCEDURE            proc_example_2
         3 TEST                 proc_example_3       PROCEDURE            proc_example_3
         4 SYS                  DBMS_HPROF           PACKAGE BODY         STOP_PROFILING
    5 TEST                 proc_example_3       PROCEDURE            __static_sql_exec_line5

5 rows selected.

Which can also be seen with this nice SQL from Oracle Base (Tim Hall):

SET LINESIZE 500 PAGESIZE 1000
COLUMN name FORMAT A100
SELECT RPAD(' ', (level-1)*2, ' ') || a.name AS name,
       a.subtree_elapsed_time,
       a.function_elapsed_time,
       a.calls
FROM   (SELECT fi.symbolid,
               pci.parentsymid,
               RTRIM(fi.owner || '.' || fi.module || '.' || NULLIF(fi.function,fi.module), '.') AS name,
               NVL(pci.subtree_elapsed_time, fi.subtree_elapsed_time) AS subtree_elapsed_time,
               NVL(pci.function_elapsed_time, fi.function_elapsed_time) AS function_elapsed_time,
               NVL(pci.calls, fi.calls) AS calls
        FROM   dbmshp_function_info fi
               LEFT JOIN dbmshp_parent_child_info pci ON fi.runid = pci.runid AND fi.symbolid = pci.childsymid
        WHERE  fi.runid = 1
        AND    fi.module != 'DBMS_HPROF') a
CONNECT BY a.parentsymid = PRIOR a.symbolid
START WITH a.parentsymid IS NULL;


NAME                                                SUBTREE_ELAPSED_TIME FUNCTION_ELAPSED_TIME      CALLS
--------------------------------------------------- -------------------- --------------------- ----------
TEST.proc_example_1                                                31262                    31          1
  TEST.proc_example_2                                              31231                   133         10
    TEST.proc_example_3                                            31098                  3241        100
      TEST.proc_example_3.__static_sql_exec_line5                  27857                 27857       1000

Cheers!

Database, SQL | PLSQL

Oracle Pivot and Unpivot Operators

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Hi All!
I was reviewing some features in Oracle and, basically, every single time I review them I find something new. Seems Oracle Databases’ features are near to infinite and we frequently find some that can really add value to our solutions.

So I decided to make a serie of posts with really quick notes about each one of them.
You can see all posts in this serie in my page of posts and some others more.

Ready? Here it goes:

Pivot and Unpivot Operators

Pivoting tables are now possible in 11g through PIVOT clause. The PIVOT operator takes data in separate rows, aggregates it and converts it into columns. Prior to 11g new functions it was possible to accomplish by using DECODE combined with some aggregate function like SUM.

Also, Adding the XML keyword to the PIVOT operator allows us to convert the generated pivot results to XML format. It also makes the PIVOT a little more flexible, making possible to replace the hard coded IN clause with a subquery, or the ANY commands.

In same way, the UNPIVOT operator converts column-based data into separate rows. Some important considerations about feature:

  • Column names are required. These can be set to any name not currently in the driving table.
  • The columns to be unpivoted must be named in the IN clause.
  • By default the EXCLUDE NULLS clause is used. To override the default behavior use the INCLUDE NULLS clause.
  • The following query shows the inclusion of the INCLUDE NULLS clause.

For more information and examples: https://oracle-base.com/articles/11g/pivot-and-unpivot-operators-11gr1

Cheers!

Cloud Services, Cloud Services | Exadata | Linux, Database, SQL | PLSQL

AWS – Kill Sessions on RDS Oracle Database

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Hi all!
Today is a quick tip. Actually, just because more than once I was about to kill a session in a RDS session and it was simply not possible with my usual ALTER SYSTEM KILL SESSION scripts… 🙂

Know how to do it? Here it goes:

begin
rdsadmin.rdsadmin_util.kill(
sid => &sid,
serial => &serial);
end;
/

Putted it in a script: @killrds.sql

Cheers!

Database, SQL | PLSQL

Increase PLSQL Performance with SIMPLE_INTEGER Data Type

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Did you know the SIMPLE_INTEGER datatype is a subtype of the PLS_INTEGER datatype and can increase the speed of integer arithmetic in natively compiled code as well as in interpreted code?

Nice, right?
This is an 11g feature, so not that new… Have a look and use it!

Check below for datatype declaration example:

PLS_INTEGER:

var_old_fashioned PLS_INTEGER := 0;

SIMPLE_INTEGER:

var_new_way SIMPLE_INTEGER := 0;

Cheers!

Database, SQL | PLSQL

Oracle No Segment Indexes

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Did you know we have this? Yes, and this is since 11g.

As you know, the process of tuning SQL statements often requires the testing of alternate indexing strategies to see the effect on execution plans.

Adding extra indexes to large tables can take a considerable amount of time and disk space besides possibly changing known execution plans and possibly affecting all the application behavior.

This can be problematic when you are trying to identify problems on a production system. Some of those problems can be solved by using invisible indexes, but they still would require creation and segment allocation, but also being updated by the application itself.

To solve that, virtual indexes have no associated segment, so the creation time and associated disk space are irrelevant. In addition, it is not seen by other sessions, so it doesn’t affect the normal running of your system, similar to invisible indexes, but also don’t not even to be updated, as invisible indexes need to be.

To create the virtual index consists in simply add the NOSEGMENT clause to the CREATE INDEX statement, for example:

CREATE INDEX index_name ON table(column_name) NOSEGMENT;

However, to make the virtual index available we must set the _use_nosegment_indexes parameter. Another important mention is that the virtual indexes don’t appear in the USER_INDEXES view, but can be found in the USER_OBJECTS view.

Cheers!

Database, SQL | PLSQL

Oracle Compound Triggers

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Did you know that?

Since 11g, Oracle has something called “compound trigger”, that allows a single trigger to be used for combining actions for different timing points for a specific object.

The individual timing points share a single global declaration section, whose state is maintained for the lifetime of the statement. Once a statement ends, due to successful completion or an error, the trigger state is cleaned up. In previous releases this type of functionality was only possible by defining multiple triggers whose code and global variables were defined in a separate package.

The triggering actions are defined in the same way as any other DML trigger, with the addition of the COMPOUND TRIGGER clause. The main body of the trigger is made up of an optional global declaration section and one or more timing point sections, each of which may contain a local declaration section whose state is not maintained. For example:

CREATE OR REPLACE TRIGGER trigger_example
    FOR action ON table_name COMPOUND TRIGGER
    global_variable VARCHAR2(30);
    BEFORE STATEMENT IS BEGIN NULL; END BEFORE STATEMENT;
    BEFORE EACH ROW IS BEGIN NULL; END BEFORE EACH ROW;
    AFTER EACH ROW IS BEGIN NULL; END AFTER EACH ROW;
    AFTER STATEMENT IS BEGIN NULL; END AFTER STATEMENT;
END trigger_example;
/

A good summary with detailed information and examples can be found (as always) here: https://oracle-base.com/articles/11g/trigger-enhancements-11gr1

Cheers!

Database, SQL | PLSQL

Oracle Virtual Columns

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Hi All!
I was reviewing some features in Oracle and, basically, every single time I review them I find something new. Seems Oracle Databases’ features are near to infinite and we frequently find some that can really add value to our solutions.

So I decided to make a serie of posts with really quick notes about each one of them.
You can see all posts in this serie in my page of posts and some others more.

Ready? Here it goes:

Virtual Columns

Since 11g is possible to create columns based on functions, not physically stored on database. See the example below:

create table sales
    (
       sales_id      number,
       cust_id       number,
       sales_amt     number,
       sale_category varchar2(6)
       generated always as
       (
          case
            when sales_amt <= 10000 then 'LOW' 
            when sales_amt > 10000 and sales_amt <= 100000 then 'MEDIUM' 
            when sales_amt > 100000 and sales_amt <= 1000000 then 'HIGH'
            else 'ULTRA'
          end
       ) virtual
   );

It’s also interesting to raise that starting on Release 2, virtual columns can be used as foreign keys. Should be used as FK, not sure… but can….

Cheers!

Database, SQL | PLSQL

Oracle: Easily Decoding ROWID

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Hi all,
Recently I needed to decode the rowid so I could find some information about it, I found this bit of code that I thought useful:

SET SERVEROUTPUT ON
DECLARE
v_rid VARCHAR2(20) ;
v_type NUMBER;
v_obj NUMBER;
v_rfno NUMBER;
v_bno NUMBER;
v_rno NUMBER;
BEGIN
v_rid := 'AAAAASAABAAAADxAAb';
dbms_output.put_line('Row_ID = "'||v_rid||'"');
dbms_rowid.rowid_info(CHARTOROWID(v_rid), v_type, v_obj, v_rfno, v_bno, v_rno);
IF v_type = 0 THEN
dbms_output.put_line('RowID Type -> Restricted');
ELSE dbms_output.put_line('RowID Type -> Extended');
END IF;
dbms_output.put_line('Object ID = "'||v_obj||'"');
dbms_output.put_line('Relative File Number = "'||v_rfno||'"');
dbms_output.put_line('Block Number = "'||v_bno||'"');
dbms_output.put_line('Row Number = "'||v_rno||'"');
END;
/

Note that I have hard-coded the rowid but it is relatively easy to either edit this or indeed to incorporate this into a procedure.

Here’s the sample output

Row_ID = "AAAAASAABAAAADxAAb"
RowID Type -> Extended
Object ID = "18"
Relative File Number = "1"
Block Number = "241"
Row Number = "27"

Hope this helps!
Cheers!

Database, SQL | PLSQL

Oracle Top Growing Segments

This is the second post of a serie. First one here.

Now that you already have an idea regarding the size of the database top segments (first post), you might want to check the top growing segments, considering a specified number of days back.

You probably used some AWR information in past or generated an AWR report, at least. But if this is still new to you, AWR stands for Automatic Workload Repository. AWR is a built-in repository, used to collect, process, and maintain performance statistics for problem detection and self-tuning purposes. This gathered data is stored both in memory and in the database, and is displayed in both reports and views.

For additional information, you can check this official doc here.

We are going to use some AWR views:
– dba_hist_seg_stat: historical information captured from V$SEGSTAT about segment-level statistics.
– dba_hist_seg_stat_obj: names of the segments captured in the workload repository.

More“Oracle Top Growing Segments”