SQL validation during PL/SQL compilation

A recent posting on SQL.RU asked why Oracle doesn’t raise such errors like “ORA-00979 not a group by expression” during PL/SQL compilation. Since I couldn’t find a link to the answer (though I read about it many years ago, but I don’t remember where…), I’ve decided to post short answer:

During PL/SQL compilation Oracle checks static SQL using only:

  1. Syntactic analysis – Oracle verifies that keywords, object names, operators, delimiters, and so on are (more...)

Intra-block row chaining optimization in 12.2

I’ve wrote in previous post

4. Next row piece can be stored in the same block only with inserts. When you run update, oracle will place new row piece into another block.

But it’s not valid anymore 🙂 Since 12.2 Oracle optimizes updates too.
You can check it on 12.2 and previous version using example 4 from previous post:

Test 4

drop table test purge;
set serverout on
alter session set tracefile_identifier='test4';
 
declare
    (more...)

How to speed up slow unicode migration of a table with xmltype columns

Recently I have had an issue with slow unicode migration of the database upgraded from 10g to 12.1.0.2. The main problem was a table with xmltype: we spent about 4 hours for this table(~17GB) during test migration, though all other tables (~190GB) migrated just for about 20 minutes.
We used DMU(Database Migration Assistant for Unicode), and the root cause of the problem was update statement generated by DMU for this table:

update   (more...)

row pieces, 255 columns, intra-block row chaining in details

You may know about Intra-block row chaining which may occur when the number of columns in a table are more than 255 columns.
But do you know that intra-block chaining works with inserts only? not updates!

Documentation says:

When a table has more than 255 columns, rows that have data after the 255th column are likely to be chained within the same block. This is called intra-block chaining. A chained row’s pieces are chained together (more...)

How even empty trigger increases redo generation

Very simple example:

Test case
set feed on;
-- simple table:
create table xt_curr1 as select level a,level b from dual connect by level<=1e4;
-- same table but with empty trigger:
create table xt_curr2 as select level a,level b from dual connect by level<=1e4;
create or replace trigger tr_xt_curr2 before update on xt_curr2 for each row
begin
  null;
end;
/

set autot trace stat;
update xt_curr1 set b=a;
set autot off;

set autot trace stat;
 (more...)

8 queens chess problem: solution in Oracle SQL

This is just another solution of this problem for a chessboard, but you can choose any size of the checkerboard:

with 
 t as (select level i, cast(level as varchar2(1)) c from dual connect by level<=&d)
,x(l,s,n) as (
       select 1 l, c s, chr(97)||c||' ' from t
       union all
       select l+1, x.s||t.c, n||chr(98+l)||i||' '
       from x
            join t
                 on instr(s,c)=0
                    and not exists(select 0 from dual 
                                   where L+1 - t.i = level  (more...)

Maven: how to copy files after a build into several distribution directories

Sometimes it is convenient to copy jar-files automatically after a build into several different directories, for example if you have different config files for local tests and for office test server, then you may want to copy these files into local test directory, internal office test server and public distribution directory.
This short part of pom.xml contains 2 different methods to build UBER-JAR and copying them into 3 different directories: localtest, officetest and public

     (more...)

WINDOW NOSORT STOPKEY + RANK()

Recently I found that WINDOW NOSORT STOPKEY with RANK()OVER() works very inefficiently: http://www.freelists.org/post/oracle-l/RANKWINDOW-NOSORT-STOPKEY-stopkey-doesnt-work
The root cause of this behaviour is that Oracle optimizes WINDOW NOSORT STOPKEY with RANK the same way as with DENSE_RANK:

rnk1
create table test(n not null) as 
  with gen as (select level n from dual connect by level<=100)
  select g2.n as n
  from gen g1, gen g2
  where g1.n<=10
/
create index ix_test on test(n)
/
exec  (more...)

Thanks to all #odevchoice voters!

And special thanks to all the great people who voted for me! :)
I want to list all voters for all nomenees in one page: http://orasql.org/odevchoice/all-the-voters.html

The query (using xt_http of course :) )

with 
  finalists(category, userid, name) as (
      --                               SQL~ Voting:
      ------ ------------------ -------------------------------------------------------------------------------------
      select 'SQL'     , 6899,  'Stew Ashton      ' from dual union all
      select 'SQL'     , 6900,  'Sean Stuber      ' from dual union all
      select 'SQL'     , 6901,  'Sayan Malakshinov' from  (more...)

Oracle package for HTTPS/HTTP[version 0.2]

A couple days ago i created simple package for HTTPS/HTTP, but I’ve decided now to improve it:

  1. Timeout parameter – it would be better to control connection time;
  2. Simple page parsing with PCRE regular expressions – to speed up and simplify page parsing, because if you want to get big number matched expressions from CLOB with regexp_xxx oracle functions, you have to call these functions many times with different [occurance] parameters, passing/accessing to the (more...)