The importance of being aliased

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| Jul 20, 2018
Always check out the original article at http://www.oraclequirks.com for latest comments, fixes and updates. I was writing a query returning the indexes to be monitored for a list of schemas for those tables having fewer than 5 indexes (not counting LOB indexes) and I was surprised to see that it returned no rows. After checking what's wrong I realized that I had specified the wrong column for

Index Monitoring in Oracle Database

Applies to ONLY Oracle Database 10gR1 through to 12cR1.
In Oracle Database 12cR2, this feature is replaced.  A new blog post of this feature will be posted in due course.

Since Oracle 10g, you can monitor indexes to see if they are being used or not.  Which is very useful as indexes, consume unnecessary CPU and I/O on DML activity if not used.  Therefore, it’s recommended to monitor indexes and any unused (more...)

Optimistic Locking 7: Restartability

When we UPDATE, Oracle may find a discrepancy between the read-consistent and "current" versions of the data. If so, Oracle "restarts" the process. Our optimistic locking solution must make that happen when appropriate.

EBR – Part 10: Data Dictionary Views for Editioning Views

This is part 10 of a post series about Oracle Edition-Based Redefinition.

Visit the index page for all the parts of the series

Introduction

In a previous post I wrote about Editioning Views and their significant role in online application upgrades using EBR.
In this post we’ll see how editioning views are represented in the data dictionary views.

I’ll discuss only the USER_* views, but everything is true for the corresponding ALL_*, DBA_* and CDB_* (more...)

CSV from CLOB with field enclosures

After my post about extracting CSV without enclosures from a CLOB, here is my solution for CSV with enclosures. It wasn't easy...

Extract from CLOB with JSON objects

On AskTOM, Kim Berg Hansen recently used JSON_OBJECT to parse CLOB data in "name=value" format. I added a variant based on my work with CSV data.

ANSI dates make life easier

This post is one of a series on what I learned while not at Kscope18.

Dimitri mentioned that he learned about the ANSI date format that allows you to return a date with the expression.


Which means this
date '2018-06-10'

Is the same as
to_char('10-Jun-2018','DD-MON-YYYY')

And you'll never want to type (more...)

Extract CSV from CLOB with JSON arrays

Marc Bleron blogged about CSV CLOBs and JSON_TABLE two years ago. Here's my contribution to improve on a great idea.

Read CLOBs fast with less memory

Reading a big CLOB is like trying to eat a burger all at once: it will take you forever if you don't choke. Why not cut that CLOB into bite-size chunks? It's faster, uses less memory - and it's good table manners...

Generate JOINs among related tables

After finding the shortest "foreign key" path between two tables, I'll try to generate a SELECT statement that joins all the related tables.

Split a string again and again

I recently needed to gather multiple columns from multiple rows into one string, then split them out again. JSON_TABLE did both splits at the same time!

Foreign keys between two tables

In a comment on my post about getting all the foreign key relationships, I was asked how to get the shortest path between two tables. Not too easy...

Splitting Strings: a New Champion!

My last post on splitting strings conceded that "a combined SQL + PL/SQL solution beats the best pure SQL solution." Wrong! I didn't try JSON_TABLE.

Wrong Results with IOT, Added Column and Secondary Index

I found a “wrong results” bug yesterday, easily reproduced in 11g, 12c and 18c.

In short, we may get wrong results under the following circumstances:

  • We have an Index-Organized Table (IOT) with multi-column primary key, populated with rows
  • The table has a secondary index on part of the primary key columns
  • We add another column to the existing IOT
  • We select from the IOT while accessing it via the secondary index

Following is a simple (more...)

Long-running delete of synopses during table stats gathering

Oracle 11.2.0.4

I recently encountered one long-running session and several blocked sessions, all performing the same delete operation.

--SQL_ID dsf21kcbjqfyk
DELETE FROM SYS.WRI$_OPTSTAT_SYNOPSIS$ WHERE BO# = :B2 AND INTCOL# = :B1;

One session had been running for several hours, and the other sessions were all blocked by a row lock from the first session. Unfortunately, each of these sessions was trying to gather stats on new partitions of tables as part (more...)

EBR – Part 9: Adding a New Column

This is part 9 of a post series about Oracle Edition-Based Redefinition.

Visit the index page for all the parts of the series

Introduction

In part 7 (“Editioning Views”) I introduced our third development use case – adding a new column that represents a new business logic.

I emphasize the fact it’s a new business logic, because sometimes we add new columns that come instead of existing columns, for replacing an existing business logic. (more...)

EBR – Part 8: The Last Planned Downtime

This is part 8 of a post series about Oracle Edition-Based Redefinition.

Visit the index page for all the parts of the series

Introduction

I concluded the previous post by stating that the application code should never reference tables directly; instead, every table should be covered by an editioning view and the application code should reference the views.

Starting from Scratch?

If you start developing a new system from scratch, I strongly recommend to follow (more...)

EBR – Part 7: Editioning Views

This is part 7 of a post series about EBR.

Visit the index page for all the parts of the series

Introduction

Our next use case is adding a column that represents a new logic to the PEOPLE table, and making the corresponding changes in the PEOPLE_DL and APP_MGR packages. Of course, as we speak about EBR, the upgrade from the previous version to the new one should be online.
An online upgrade means that (more...)

Filtering outliers from Oracle APEX activity logs

Last year I described a simple test case that described how to remove outliers from a fictional dataset using the STDDEV() analytical function .
http://www.grassroots-oracle.com/2017/06/removing-outliers-using-stddev.html

I want to follow this up with a practical case using one of my favourite data sets - the apex_workspace_activity_logs that record who opened what page, in what context, and how long it took to generate.

I've been keeping an eye on the performance of a particular page, (more...)

PostgreSQL Calling File

Somebody asked: How do you run a script file from PostgreSQL’s psql prompt? I created two files to answer the question. Here are the two files:

Static File

SELECT 'Hello World!';

Dynamic File

SELECT 'Hello ['||current_user||']!';

It’s a simple solution, you put a \i or \include before the script file name, like:

\i helloworld.sql

or

\include hellowhom.sql

I hope this helps those trying to call SQL script files from an interactive psql session.