12cR2 tightens up ORA-01841 for zero year ANSI dates, but not for Oracle SQL syntax

In moving some more code from an 11gR2 database to a 12cR2 database, I found another change where a piece of code that works in 11gR2 doesn’t compile in 12cR2.

In this instance a view was being created with a projected date column which used the ANSI DATE syntax. Here is a simplified test script:

CREATE OR REPLACE VIEW test1 AS
SELECT date '0000-01-01' date_col
FROM dual
/
DROP VIEW test
/

CREATE OR REPLACE VIEW test2 AS
SELECT TO_DATE('0000-01-01','YYYY-MM-DD') date_col
FROM dual
/

Running this on 11gR2 gives:

SQL>CREATE OR REPLACE VIEW test1 AS
  2  SELECT date '0000-01-01' date_col
  3  FROM   dual
  4  /

View created.

SQL>CREATE OR REPLACE VIEW test2 AS
  2  SELECT TO_DATE('0000-01-01','YYYY-MM-DD') date_col
  3  FROM   dual
  4  /

View created.

Now running this on 12cR2 gives:

SQL> CREATE OR REPLACE VIEW test1 AS
  2  SELECT date '0000-01-01' date_col
  3  FROM   dual
  4  /
SELECT date '0000-01-01' date_col
            *
ERROR at line 2:
ORA-01841: (full) year must be between -4713 and +9999, and not be 0


SQL> CREATE OR REPLACE VIEW test2 AS
  2  SELECT TO_DATE('0000-01-01','YYYY-MM-DD') date_col
  3  FROM   dual
  4  /

View created.

The date is zero and thus the error message is correct in 12cR2 for the ANSI DATE syntax.

ORA-54002 when trying to create Virtual Column using REGEXP_REPLACE on Oracle 12cR2

I encountered an issue today trying to create a table in an Oracle 12cR2 database, the DDL for which, I extracted from an Oracle 11gR2 database. The error returned when trying to create the table was:

ORA-54002: only pure functions can be specified in a virtual column expression

The definition of the table included a Virtual Column which used a REGEXP_REPLACE call to derive a value from another column on the table.

Here is a simplified test case illustrating the scenario (Thanks Tim for the REGEXP_REPLACE example code):

select * from v$version
/
create table test_ora54002_12c(
 col1 VARCHAR2(20 CHAR) NOT NULL
 ,virtual_column1 VARCHAR2(4000 CHAR) GENERATED ALWAYS AS(REGEXP_REPLACE(col1, '([A-Z])', ' \1', 2)) VIRTUAL VISIBLE
)
/
drop table test_ora54002_12c purge
/

Running this on 11gR2 gives:

SQL> select * from v$version
 2 /

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
PL/SQL Release 11.2.0.4.0 - Production
CORE 11.2.0.4.0 Production
TNS for Linux: Version 11.2.0.4.0 - Production
NLSRTL Version 11.2.0.4.0 - Production

5 rows selected.

Elapsed: 00:00:00.40
SQL> create table test_ora54002_12c(
 2 col1 VARCHAR2(20 CHAR) NOT NULL
 3 ,virtual_column1 VARCHAR2(4000 CHAR) GENERATED ALWAYS AS(REGEXP_REPLACE(col1, '([A-Z])', ' \1', 2)) VIRTUAL VISIBLE
 4 )
 5 /

Table created.

Elapsed: 00:00:00.24
SQL> drop table test_ora54002_12c purge
 2 /

Table dropped.

Running this on 12cR2 gives:

SQL> select * from v$version
/
 2
BANNER CON_ID
-------------------------------------------------------------------------------- ----------
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production 0
PL/SQL Release 12.2.0.1.0 - Production 0
CORE 12.2.0.1.0 Production 0
TNS for Linux: Version 12.2.0.1.0 - Production 0
NLSRTL Version 12.2.0.1.0 - Production 0

SQL> create table test_ora54002_12c(
 col1 VARCHAR2(20 CHAR) NOT NULL
 ,virtual_column1 VARCHAR2(4000 CHAR) GENERATED ALWAYS AS(REGEXP_REPLACE(col1, '([A-Z])', ' \1', 2)) VIRTUAL VISIBLE
)
/
 2 3 4 5 ,virtual_column1 VARCHAR2(4000 CHAR) GENERATED ALWAYS AS(REGEXP_REPLACE(col1, '([A-Z])', ' \1', 2)) VIRTUAL VISIBLE
 *
ERROR at line 3:
ORA-54002: only pure functions can be specified in a virtual column expression


SQL> drop table test_ora54002_12c purge
/
 2 drop table test_ora54002_12c purge
 *
ERROR at line 1:
ORA-00942: table or view does not exist

As you can see, 12cR2 gives the ORA-54002 error.

Looking on MOS, highlights this article, which suggests that you shouldn’t have been able to do this in 11gR2, i.e. it was a bug and that 12cR2 has fixed this bug and thus you can no longer create such a virtual column (the article refers to functional index and check constraint use cases as well).

In my case, I was able to rewrite the virtual column to use simple string functions such as SUBSTR, TRANSLATE and INSTR to achieve what I wanted and the virtual column was allowed to be created with these – problem solved – a shame really as the REGEXP_REPLACE approach was far neater.

Create Jupyterhub Container on Centos 7 on Proxmox

These instructions show how to create a Centos 7 container on Proxmox running JupyterHub.

Note – the instructions are just a guide and for use on my environment – you may need/wish to adjust for your own environment as necessary.

Versions

root@billy:~# pveversion
pve-manager/4.4-12/e71b7a74 (running kernel: 4.4.40-1-pve)
The version of the notebook server is 4.4.1
Python 3.4.5 (default, Nov  9 2016, 16:24:59) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-11)]

Create Container

pct create 153 u01:vztmpl/centos-7-default_20160205_amd64.tar.xz -rootfs 10 -hostname jupyterhub -memory 2048 -nameserver 192.168.1.25 -searchdomain oramoss.com -net0 name=eth0,bridge=vmbr0,gw=192.168.1.1,ip=192.168.1.153/24 -swap 2048 -cpulimit 2 -storage u01

Installation

Update system

yum update -y
yum install epel-release -y
yum install
wget http://public-yum.oracle.com/RPM-GPG-KEY-oracle-ol7 -O /etc/pki/rpm-gpg/RPM-GPG-KEY-oracle 

Install JDK

wget -y cd ~ wget --no-cookies --no-check-certificate --header "Cookie: gpw_e24=http%3A%2F%2Fwww.oracle.com%2F; oraclelicense=accept-securebackup-cookie" "http://download.oracle.com/otn-pub/java/jdk/8u111-b14/jdk-8u111-linux-x64.rpm" 
yum localinstall jdk-8u111-linux-x64.rpm -y 
rm -f ~/jdk-8u111-linux-x64.rpm 
vi /etc/environment export 
 JAVA_HOME=/usr/java/jdk1.8.0_111/jre 
vi ~/.bash_profile 
 export PATH=${JAVA_HOME}/bin:$PATH 
. ~/.bash_profile 
java -version 

Install Oracle 7 Linux repo (works for Centos 7)

wget http://yum.oracle.com/public-yum-ol7.repo yum 

Install Python 3 And Jupyter Notebook

install python34 -y 
curl -O https://bootstrap.pypa.io/get-pip.py /usr/bin/python3.4 get-pip.py 
yum install npm nodejs-legacy -y
yum install anaconda -y 
python3 -m pip install jupyterhub 
npm config set strict-ssl false 
npm install -g configurable-http-proxy 
python3 -m pip install notebook 
wget ftp://ftp.icm.edu.pl/vol/rzm5/linux-slc/centos/7.0.1406/cernonly/x86_64/Packages/oracle-instantclient12.1-basic-12.1.0.2.0-1.x86_64.rpm 
wget ftp://bo.mirror.garr.it/1/slc/centos/7.1.1503/cernonly/x86_64/Packages/oracle-instantclient12.1-sqlplus-12.1.0.2.0-1.x86_64.rpm 
wget ftp://bo.mirror.garr.it/1/slc/centos/7.1.1503/cernonly/x86_64/Packages/oracle-instantclient12.1-devel-12.1.0.2.0-1.x86_64.rpm 
yum install oracle-instantclient12.1-basic-12.1.0.2.0-1.x86_64.rpm -y 
yum install oracle-instantclient12.1-devel-12.1.0.2.0-1.x86_64.rpm -y 
yum install oracle-instantclient12.1-sqlplus-12.1.0.2.0-1.x86_64.rpm -y 
vi ~/.bash_profile 
  export ORACLE_HOME=/usr/lib/oracle/12.1/client64 
  export PATH=$ORACLE_HOME/bin:$PATH 
  export LD_LIBRARY_PATH=$ORACLE_HOME/lib:$LD_LIBRARY_PATH 
vi /etc/environment 
  export ORACLE_HOME=/usr/lib/oracle/12.1/client64 
  export PATH=$ORACLE_HOME/bin:$PATH 
  export LD_LIBRARY_PATH=$ORACLE_HOME/lib:$LD_LIBRARY_PATH 
. ~/.bash_profile 
yum install gcc -y 
yum install python-devel -y 
yum install python34-devel -y 
pip install cx_Oracle
pip install ipython-sql 
jupyterhub --generate-config 
vi /root/jupyterhub_config.py # ensure the following are set: 
  c.Spawner.env_keep = ['LD_LIBRARY_PATH'] 
  c.Spawner.environment = dict(LD_LIBRARY_PATH='/usr/lib/oracle/12.1/client64/lib:$LD_LIBRARY_PATH') 
systemctl stop firewalld 
systemctl disable firewalld 
vi /lib/systemd/system/jupyterhub.service 
  [Unit] 
  Description=Jupyterhub 
  After=network-online.target 
  [Service] 
  User=root ExecStart=/usr/bin/jupyterhub --ip=192.168.1.10 
  WorkingDirectory=/root 
  [Install] 
  WantedBy=multi-user.target 
systemctl enable jupyterhub 
systemctl start jupyterhub 
systemctl status jupyterhub

That should be it…navigate to http://192.168.1.153:8000 and login with a unix user on that node.

Installing Oracle 12c Release 2 Database on a Proxmox Container

Obviously nobody could beat Tim to getting the comprehensive installation instructions out first, but here are my notes for installing it on a proxmox container environment which is what I use as my research platform. Some of the calls used are from or based on Tim’s prior 12cR1 installation article – thanks Tim.

NOTE – this post is just a guide and is based on my environment – you will likely need to make changes to suit your own environment.

Environment

root@billy:~# pveversion
pve-manager/4.4-12/e71b7a74 (running kernel: 4.4.40-1-pve)

Host Preparation

Some of the activities required involve changing linux parameters but these can’t be applied inside a proxmox container – you’ll see errors like these if you try:

[root@db12cr2 ~]# sysctl -p
sysctl: setting key "fs.file-max": Read-only file system

Instead you have to do these at the host level – and only if you think they are relevant and that those settings wouldn’t upset all of your other environments running on that host. I haven’t tried but you could potentially just tell the GUI installer to ignore the warnings relating to these entries and not make these changes at all especially if you’re only using it for small scale research purposes.

As root on the proxmox host, run the following:

echo "fs.file-max = 6815744" >>/etc/sysctl.d/98-oracle.conf
echo "kernel.panic_on_oops = 1" >>/etc/sysctl.d/98-oracle.conf
echo "net.ipv4.conf.default.rp_filter = 2" >>/etc/sysctl.d/98-oracle.conf
/sbin/sysctl -p

Create And Prepare The Container

I use Centos 7 as the template for most of my activities and these notes are based around that.

pct create 130 u01:vztmpl/centos-7-default_20160205_amd64.tar.xz -rootfs 60 -hostname db12cr2 -memory 10240 -nameserver 192.168.1.25 -searchdomain oramoss.com -net0 name=eth0,bridge=vmbr0,gw=192.168.1.1,ip=192.168.1.130/24 -swap 10240 -cpulimit 4 -storage local

You’ll have your own way of getting the installation files to be available to the container but I do it by adding a mount point so I can access the area where all my software is:

vi /etc/pve/nodes/${HOSTNAME}/lxc/130.conf

…and add this:

mp0: /mnt/backups/common_share,mp=/mnt/common_share

Start And Enter The Container

pct start 130
pct enter 130

Install Additional Packages

I’m going to use the Oracle Preinstall package but there are still a few things to add:

yum install gcc-c++ wget openssh-server -y

gcc-c++ is not necessary according to the 12cR2 installation manuals, but the GUI installer complains during the prerequisite checks if it’s not there.

wget is needed to download some files and it’s not on the Centos 7 template.

openssh server is to allow me to login remotely via SSH for the GUI install later.

Get OpenSSH To Autostart

systemctl enable sshd.service
systemctl start sshd.service
systemctl status sshd.service

Install Oracle Preinstall Package

#Get the Oracle Linux 7 repo - this works for Centos 7.
cd /etc/yum.repos.d/ 
wget http://public-yum.oracle.com/public-yum-ol7.repo
#The following stops GPG Key errors:
wget http://public-yum.oracle.com/RPM-GPG-KEY-oracle-ol7 -O /etc/pki/rpm-gpg/RPM-GPG-KEY-oracle
#Update everything
yum update -y
#Install the preinstall package
yum install oracle-database-server-12cR2-preinstall -y

Configure System Limits

echo "oracle soft nofile 1024" >>/etc/security/limits.d/oracle-rdbms-server-12cR2-preinstall.conf
echo "oracle hard nofile 65536" >>/etc/security/limits.d/oracle-rdbms-server-12cR2-preinstall.conf
echo "oracle soft nproc 16384" >>/etc/security/limits.d/oracle-rdbms-server-12cR2-preinstall.conf
echo "oracle hard nproc 16384" >>/etc/security/limits.d/oracle-rdbms-server-12cR2-preinstall.conf
echo "oracle soft stack 10240" >>/etc/security/limits.d/oracle-rdbms-server-12cR2-preinstall.conf
echo "oracle hard stack 32768" >>/etc/security/limits.d/oracle-rdbms-server-12cR2-preinstall.conf
echo "oracle hard memlock 134217728" >>/etc/security/limits.d/oracle-rdbms-server-12cR2-preinstall.conf
echo "oracle soft memlock 134217728" >>/etc/security/limits.d/oracle-rdbms-server-12cR2-preinstall.conf

Change Password For “oracle” User

passwd oracle
   <<set a password>>

Create Oracle Home Directory

mkdir -p /u01/app/oracle/product/12.2.0.1/db_1
chown -R oracle:oinstall /u01
chmod -R 775 /u01

Modify The Profile Of “oracle” User

echo "# Oracle Settings" >>/home/oracle/.bash_profile
echo "export TMP=/tmp" >>/home/oracle/.bash_profile
echo "export TMPDIR=\$TMP" >>/home/oracle/.bash_profile
echo "export ORACLE_HOSTNAME=db12cr2.oramoss.com" >>/home/oracle/.bash_profile
echo "export ORACLE_UNQNAME=cdb1" >>/home/oracle/.bash_profile
echo "export ORACLE_BASE=/u01/app/oracle" >>/home/oracle/.bash_profile
echo "export ORACLE_HOME=\$ORACLE_BASE/product/12.2.0.1/db_1" >>/home/oracle/.bash_profile
echo "export ORACLE_SID=cdb1" >>/home/oracle/.bash_profile
echo "export PATH=/usr/sbin:\$PATH" >>/home/oracle/.bash_profile
echo "export PATH=\$ORACLE_HOME/bin:\$PATH" >>/home/oracle/.bash_profile
echo "export LD_LIBRARY_PATH=\$ORACLE_HOME/lib:/lib:/usr/lib" >>/home/oracle/.bash_profile
echo "export CLASSPATH=\$ORACLE_HOME/jlib:\$ORACLE_HOME/rdbms/jlib" >>/home/oracle/.bash_profile

Create Software Directory And Copy Files Over

mkdir -p /u01/software
cp /mnt/common_share/linuxx64_12201_database.zip /u01/software
unzip linuxx64_12201_database.zip
rm /u01/software/linuxx64_12201_database.zip

Run The Installer

Log in as the “oracle” user

cd /u01/software/database
./runInstaller

Install the software and a database by running through the GUI screens and following the instructions. The installer complains on the prerequisite checks screen about some of the kernel memory parameters (rmem%, wmem%) which you can ignore.

Configure Auto Start

Follow these instructions from Tim to setup auto start using the runuser method – make sure you change the ORACLE_HOME to be 12.2.0.1 not 12.1.0.2 that is mentioned.

Now reboot the container and it should return with the database automatically started.

Check Oracle Database Auto Starts

[oracle@db12cr2 ~]$ sqlplus /nolog

SQL*Plus: Release 12.2.0.1.0 Production on Thu Mar 2 14:16:53 2017

Copyright (c) 1982, 2016, Oracle. All rights reserved.

SQL> conn sys/Password01 as sysdba
 Connected.
 SQL> show sga

Total System Global Area 3221225472 bytes
 Fixed Size 8797928 bytes
 Variable Size 687866136 bytes
 Database Buffers 2516582400 bytes
 Redo Buffers 7979008 bytes
 SQL>

Conclusion

All pretty painless and relatively quick. I’ll take a dump of the container next in order to use it as a template for building future containers.

Creating Oracle Big Data Lite VM on Proxmox

The Oracle Big Data Lite VM available on Oracle technet, provides a pre built environment for learning about a number of key Oracle products, including Oracle 12c database, Big Data Discovery and Data integrator as well as Cloudera Distribution – Apache Hadoop (CDH 5.8.0).

The download ultimately delivers an OVA “appliance” file for use with Oracle VirtualBox, but there isn’t anything to stop you running this as a VM on proxmox 4, with a bit of effort, as follows.

NOTE – Things to read which can help with this process:

  1. Oracle Big Data Lite Deployment Guide.
  2. How to upload an OVA to proxmox guide by James Coyle: https://www.jamescoyle.net/how-to/1218-upload-ova-to-proxmox-kvm
  3. Converting to RAW and pushing to a raw lvm partition: https://www.nnbfn.net/2011/03/convert-kvm-qcow2-to-lvm-raw-partition/
  • Firstly download the files that make up the OVA from here.
  • Follow the instructions on the download page to convert the multiple files into one single OVA file.
  • For Oracle Virtualbox, simple follow the rest of the instructions in the Deployment Guide.
  • For Proxmox, where I was running LVM storage for the virtual machines, first rename the single OVA file to .ISO, then upload that file (BigDataLite460.iso) to a storage area on your proxmox host, in this case, mine was called “data”. You can upload the file through the Proxmox GUI, or manually via the command line. My files were uploaded through the GUI and end up in “/mnt/pve-data/template/iso”.
  • Now, bring up a shell and navigate to the ISO directory and then unpack the ISO file by running “tar xvf BigDataLite460.iso”. This should create five files which include one OVF file (Open Virtualisation Format) and four VMDK files (Virtual Machine Disk).
root@HP20052433:/mnt/pve-data/template/iso# ls -l
total 204127600
-rw------- 1 root root   8680527872 Oct 25 02:43 BigDataLite460-disk1.vmdk
-rw------- 1 root root   1696855040 Oct 25 02:45 BigDataLite460-disk2.vmdk
-rw------- 1 root root  23999689216 Oct 25 03:11 BigDataLite460-disk3.vmdk
-rw------- 1 root root       220160 Oct 25 03:11 BigDataLite460-disk4.vmdk
-rw-r--r-- 1 root root  34377315328 Nov 14 10:59 BigDataLite460.iso
-rw------- 1 root root        20056 Oct 25 02:31 BigDataLite460.ovf
  • Now, create a new VM in proxmox via the GUI or manually. The VM I created had the required memory and CPUs as per the deployment guide, together with four Hard Disks – mine were all on the SCSI interface and were set to be 10G in size initially – this will change later.
  • The hard disks were using a storage area on Proxmox that was defined as type LVM.
  • Now convert the VMDK files to RAW files which we’ll then push to the LVM Hard Disks as follows:
qemu-img convert -f vmdk BigDataLite460-disk1.vmdk -O raw BigDataLite460-disk1.raw
qemu-img convert -f vmdk BigDataLite460-disk2.vmdk -O raw BigDataLite460-disk2.raw
qemu-img convert -f vmdk BigDataLite460-disk3.vmdk -O raw BigDataLite460-disk3.raw
qemu-img convert -f vmdk BigDataLite460-disk4.vmdk -O raw BigDataLite460-disk4.raw
  • Now list those raw files, so we can see their sizes:
root@HP20052433:/mnt/pve-data/template/iso# ls -l *.raw
-rw-r--r-- 1 root root 104857600000 Nov 16 07:58 BigDataLite460-disk1.raw
-rw-r--r-- 1 root root 214748364800 Nov 16 08:01 BigDataLite460-disk2.raw
-rw-r--r-- 1 root root 128849018880 Nov 16 08:27 BigDataLite460-disk3.raw
-rw-r--r-- 1 root root  32212254720 Nov 16 08:27 BigDataLite460-disk4.raw
  • Now resize the lvm hard disks to the corresponding sizes (the ID of my proxmox VM was 106 and my hard disks were scsi):
qm resize 106 scsi0 104857600000
qm resize 106 scsi1 214748364800
qm resize 106 scsi2 128849018880
qm resize 106 scsi3 32212254720
  • Now copy over the content of the raw files to the corresponding lvm hard disks:
dd if=BigDataLite460-disk1.raw of=/dev/vm_storage_group/vm-106-disk-1
dd if=BigDataLite460-disk2.raw of=/dev/vm_storage_group/vm-106-disk-2
dd if=BigDataLite460-disk3.raw of=/dev/vm_storage_group/vm-106-disk-3
dd if=BigDataLite460-disk4.raw of=/dev/vm_storage_group/vm-106-disk-4
  • Now start the VM and hey presto there it is.
  • You could stop there as it’s a self contained environment, but obviously you can also do a whole bunch of networking stuff to make it visible on your network as well.

OTN Appreciation Day: Automatic Storage Management (ASM)

Big shout out to Tim for kicking this off!

Automatic Storage Management (ASM) provides optimised volume management and filesystem capabilities for Oracle databases, whether they be single or multi instance (RAC) implementations.

Although introduced with Oracle 10g Release 1 in 2004, I first used it in a production scenario around 2008, when upgrading a hardware platform for a Data Warehouse. It seemed like a logical choice for myself and the DBAs at the time, although the storage team were less pleased at losing some control. Ultimately it proved a big success on that project and is still in stable, reliable use today.

Things I like about ASM include:

  • Simplifies storage management
  • Automatic rebalancing when capacity is added
  • Visibility within Enterprise Manager for monitoring
  • Availability of detailed metrics within the database
  • Reliable, balanced and consistent performance
  • Works with RAC
  • Rolling upgrades and patching
  • Provides a reliable cluster filesystem (ACFS)
  • Even more cool features coming in 12c such as Flex ASM

 

Some useful links:

ASM Administrators Guide 12cR1 (Oracle Docs)

The Mother Of All ASM Scripts (John Hallas)

Technical overview of new features for ASM in 12c (Whitepaper)

Transferring default domains for SQL Developer Data Modeler

I got a new laptop the other day and installed all the software, including SQL Developer Data Modeler all fine. I then opened a model which had a bunch of tables with columns based off Domains…the columns did not have Domains against them but had been replaced with Logical data types instead.

After some research, the fix, in this case, involved copying the file “defaultdomains.xml” from the following directory on my old laptop, to the same place on the new laptop:

%SQL Developer Home%\sqldeveloper\extensions\oracle.datamodeler\types

After restarting and reopening the model all was back to normal.

What I probably could have done in the first place was to have created my own Domains file for the Design, saved in the Design folder and then when I transferred the Design by copying across the Design folder the domains would have come with it. I could have then just opened the Domain file on the new laptop. I guess it depends on whether I would want these domains to Design specific or part of the defaults.

Transferring default domains for SQL Developer Data Modeller

Notice: You are using wrong way to display KC Content, Correct It Now

I got a new laptop the other day and installed all the software, including SQL Developer Data Modeller all fine. I then opened a model which had a bunch of tables with columns based off Domains…the columns did not have Domains against them but had been replaced with Logical data types instead.

After some research, the fix, in this case, involved copying the file “defaultdomains.xml” from the following directory on my old laptop, to the same place on the new laptop:

%SQL Developer Home%\sqldeveloper\extensions\oracle.datamodeler\types

After restarting and reopening the model all was back to normal.

What I probably could have done in the first place was to have created my own Domains file for the Design, saved in the Design folder and then when I transferred the Design by copying across the Design folder the domains would have come with it. I could have then just opened the Domain file on the new laptop. I guess it depends on whether I would want these domains to be Design specific or part of the defaults for all designs.

Oracle Virtual Columns – Can’t use plain column or duplicate expressions

I had a scenario today where I was loading a table and a particular column is known by multiple names in different source systems and thus to different people. In order to make everyone happy on this occasion, I wondered if I could create a normal column for one of the multiple names and then use virtual columns pointing at the normal column, for the other names.

I’m aware there are several ways of skinning this cat and that virtual columns was probably not the best choice in the first place, but I was just playing with an idea and it didn’t quite end up where I thought…so it was interesting in that respect.

The test code:


CREATE TABLE test
  (
     column1    INTEGER NOT NULL 
    ,virtual_column1 INTEGER AS ( column1 ) VIRTUAL NOT NULL 
  )
/
CREATE TABLE test
  (
     column1    INTEGER NOT NULL 
    ,virtual_column1 INTEGER AS ( column1 + 0 ) VIRTUAL NOT NULL 
  )
/
DROP TABLE test PURGE
/
CREATE TABLE test
  (
     column1    INTEGER NOT NULL 
    ,virtual_column1 INTEGER AS ( column1 + 0 ) VIRTUAL NOT NULL 
    ,virtual_column2 INTEGER AS ( column1 + 0 ) VIRTUAL NOT NULL 
  )
/
CREATE TABLE test
  (
     column1    INTEGER NOT NULL 
    ,virtual_column1 INTEGER AS ( column1 + 0 ) VIRTUAL NOT NULL 
    ,virtual_column2 INTEGER AS ( column1 + 1 - 1 ) VIRTUAL NOT NULL 
  )
/
DROP TABLE test PURGE
/

And the results:


    ,virtual_column1 INTEGER AS ( column1 ) VIRTUAL NOT NULL
                                  *
ERROR at line 4:
ORA-54016: Invalid column expression was specified



Table created.


Table dropped.

    ,virtual_column2 INTEGER AS ( column1 + 0 ) VIRTUAL NOT NULL
     *
ERROR at line 5:
ORA-54015: Duplicate column expression was specified



Table created.


Table dropped.

I expected it to just work, but I clearly ran in to two problems which scuppered my idea. Firstly, the virtual column can’t simply refer to a normal column without any changes to it, otherwise it fails with ORA-54016. The error isn’t particularly helpful, but eventually I worked out that it was because the column is simply a mapping to a non virtual column. Working around that by adding zero to the numeric column gets it to work, but it’s an ugly hack.

In my scenario there are three different names for this column, depending on the users involved, which then leads on to the next issue, which is that I’d then need two virtual columns pointing at the same source column. Unfortunately if I use the same hack twice, it fails with ORA-54015, because you can’t have two virtual columns with exactly the same expression! A slight variant to the hack and it works, but it’s getting uglier and uglier!

Time to seek out plan B!