More Than Four

Areas of Interest, as counted by my cat

Page 2 of 12

Changing Source Control providers

For the last few years we’ve used Assembla to host source control (Subversion) for one of our projects. We signed up for a free hosting plan, and later on, when Assembla switched to pay-only plans, they graciously allowed us to continue using them for no charge. We knew we were on borrowed time, however.

This week I received a nicely-worded email from them indicating that it was time for us to upgrade to a paid plan, or transition to a different provider. After reviewing the paid options, we decided to find someone else to host our project. We have very modest requirements, and the offerings from Assembla were somewhat more than we needed.

Apart from that, we have no complaints about Assembla – they’re awesome, and if one of their plans fits your needs, I say go for it.

However, for our little project, RiouxSVN was looking like a better fit. I decided to give them a try.

How much?

For no cost, you get 50 MB of storage for up to 4 repositories. Well, we had one repository, but it was (according to Assembla) 75 MB in size. RiouxSVN gives you the tools to upgrade various aspects of your account, through redemption of credits. What is a credit? It’s what you get if you donate to RiouxSVN (via PayPal). $1 gets you 1 credit.

If you want 20 MB of additional storage, that uses 1 credit. Want another repository slot? That’s 2 credits. If you delete a repository, you get back the credits used to augment it, allowing you to re-allocate them. Nice.

I used 4 credits to pump up the available storage to 130 MB. That’s permanent – it’s one-time, not an annual donation. That’s nice.

Migration

OK, so the next step is to migrate our repository from Assembla to RiouxSVN.

After some research, I determined that the best option for us was a two-step process: to export to a local dump file, and then import the dump file. As a long-time, but not very deep TortoiseSVN user, I needed to install the latest command-line tools for the export/import task. I selected SlikSVN for this purpose.

The export, using svnrdump, is simple:

cd c:\temp
mkdir svn_dump
cd svn_dump
svnrdump dump https://subversion.assembla.com/svn/MyProject/trunk > MyProject.svn_dump
* Dumped revision 0.
* Dumped revision 1.
* Dumped revision 2.
:

After about 2-3 minutes, I had a 105 MB dump file.

Importing was basically the same process, only this time I was prompted for my RiouxSVN account credentials:

svnrdump load https://svn.riouxsvn.com/MyProject < MyProject.svn_dump
Authentication realm: <https://svn.riouxsvn.com:443> RiouxSVN
Username: xxxxxx
Password for 'xxxxxx': ************
* Loaded revision 0.
* Loaded revision 1.
* Loaded revision 2.
:

This took longer, a couple of seconds per revision. After about 10 minutes, it was completed. And I verified I could check out, check in, and commit a simple change to the new repository.

SQL Server 2017 on Linux Mint

I followed the instructions as laid out here:

My target was a VM instance of Linux Mint 18.3, called “golem”. Everything just works… SQL Server is running automatically after I boot the VM.

Some other links I need to review:

Interestingly, the database properties don’t seem to know about the Linux host:

image

Fart-ing forward slashes

I have a home-grown database build script that allows me to build multiple instances of my database.

The build scripts allow me to target a number of different environments (test, dev, etc) and perform upgrade or replace operations.

I use the wonderful FART utility to perform text substitution into templated script files, using placeholders delimited with @@. (FART is a command-line utility developed by Lionello Lunesu. The name is an acronym for “Find-And-Replace-Text”. )

For example, consider the following template script, build.tpl:

create database @@DB_NAME@@
containment = partial
on primary
( name = '@@DB_NAME@@',
filename = '@@DATA_PATH@@@@DB_NAME@@.mdf',
size = 5120KB,
filegrowth = 1024KB
)
log on
( name = '@@DB_NAME@@_log',
filename = '@@LOG_PATH@@@@DB_NAME@@_log.ldf',
size = 1024KB,
filegrowth = 10%
)
collate Latin1_General_CS_AS;
go

This template can be written out as a targeted script using a sequence of command-line instructions:

copy build.tpl build.sql

set SB_DB_NAME=MY_NEW_DB
set SB_DATA_PATH=c:\SQL\Data\
set SB_LOG_PATH=C:\SQL\Log\

fart *.sql @@DB_NAME@@ %SB_DB_NAME%
fart *.sql @@DATA_PATH@@ %SB_DATA_PATH%
fart *.sql @@LOG_PATH@@ %SB_LOG_PATH%

Running this yields the following output:

build.sql
Replaced 5 occurence(s) in 1 file(s).

build.sql
Replaced 1 occurence(s) in 1 file(s).

build.sql
Replaced 1 occurence(s) in 1 file(s).

And the contents of build.sql is now:

create database MY_NEW_DB
containment = partial
on primary
( name = 'MY_NEW_DB',
filename = 'C:\SQL\Data\MY_NEW_DB.mdf',
size = 5120KB,
filegrowth = 1024KB
)
log on
( name = 'MY_NEW_DB_log',
filename = 'C:\SQL\Log\MY_NEW_DB_log.ldf',
size = 1024KB,
filegrowth = 10%
)
collate Latin1_General_CS_AS;
go

This is now ready to execute as part of the larger automated build process (This is obviously a simplified example.)

This is all fine and dandy until we try to target a brand new instance of SQL Server 2017 running on Linux. (Distribution of choice: Mint). The paths need to be changed to the unix-style with forward slashes:

set SB_DB_NAME=MY_NEW_DB
set SB_DATA_PATH=/var/opt/mssql/data/
set SB_LOG_PATH=/var/opt/mssql/data/

You’d think this would Just Work, but unfortunately we get an error:

build.sql
Replaced 5 occurence(s) in 1 file(s).

> fart *.sql @@DATA_PATH@@ %SB_DATA_PATH%
Error: invalid option -/
Error: invalid option -o
Error: invalid option -t
Error: invalid option -/
Error: invalid option -m
Error: invalid option -l
Error: invalid option -/
Error: invalid option -d
Error: invalid option -t
Error: invalid option -/

We have to escape the slashes, and also tell FART to use c-style extended characters, with the -C switch:

set SB_DB_NAME=MY_NEW_DB
set SB_DATA_PATH=\/var\/opt\/mssql\/data\/
set SB_LOG_PATH=\/var\/opt\/mssql\/data\/

fart *.sql @@DB_NAME@@ %SB_DB_NAME%
fart -C *.sql @@DATA_PATH@@ %SB_DATA_PATH%
fart -C *.sql @@LOG_PATH@@ %SB_LOG_PATH%

This looks a bit odd, and the output to console includes a warning message:

Warning: unrecognized character escape sequence: \/
Warning: unrecognized character escape sequence: \/
Warning: unrecognized character escape sequence: \/
Warning: unrecognized character escape sequence: \/
Warning: unrecognized character escape sequence: \/
build.sql
Replaced 1 occurence(s) in 1 file(s).

Warning: unrecognized character escape sequence: \/
Warning: unrecognized character escape sequence: \/
Warning: unrecognized character escape sequence: \/
Warning: unrecognized character escape sequence: \/
Warning: unrecognized character escape sequence: \/
build.sql
Replaced 1 occurence(s) in 1 file(s).

However, the substitution did take place, and the result is correct:

create database MY_NEW_DB
containment = partial
on primary
( name = 'MY_NEW_DB',
filename = '/var/opt/mssql/data/MY_NEW_DB.mdf',
size = 5120KB,
filegrowth = 1024KB
)

etc.

This console warning message is probably a bug in FART.

UPDATE: And someone else has already reported it: #12 Warning: unrecognized character escape sequence: \/.

Virtuabox Host Networking revisited

My current work environment consists of a Windows 10 host running Virtualbox 5.2 with a Windows 7 guest VM,in which I run my client development tools.

I had Virtualbox Host Networking set up on the default 192.168.56.x subnet, but the second adapter in the guest wasn’t configured because at the time I had no need to “see” the host resources from the guest.

Until now… I find that I needed to point some client tools on the guest VM at the SQL Server instance running on the host.

Okay, no problem, just set up the second adaptor on the guest as 192.168.56.56, set the gateway as 56.1, and it should all work, right?

image

Yeah, well, for some reason it did not work. I could PING the guest from the host side, but the host was not responding to pings from the guest.

Temporarily disabling the Windows Firewall on the host allowed the guest to “see” the host. So it was a Windows 10 host firewall configuration issue.

I found this post that explains how best to address this problem:

https://superuser.com/questions/936581/how-to-config-windows-firewall-so-vm-host-only-can-ping-windows-7

Essentially:

  • Open Windows Firewall
  • Scroll the right-hand pane down until you see “Windows Firewall Properties”
  • Click on it
  • Select Public Profile
  • Click on “Customize”
  • un-check the “Virtualbox Host Only Network”

image

This will disable Windows Firewall from getting in the way of networking between the host and guest.

Thanks, Andrew Joe!

Upgrading site from BlogEngine 2.5 to 3.3

I though this was going to be a nightmare, but getting the content moved from 2.5 to 3.3 was the easiest part, using the BlogML export and import. The tricky part was adapting the Standard theme to match my previously customized one. A straight copy of the theme folder did not work.

This will do for now.

Flyway DB

For years I’ve used a database build script framework written in-house to recompile all schema objects and run unit tests. However, the actual DDL code to migrate a schema from one version to the next was always left as a hand-rolled script that is executed up-front before the normal build process.

A colleague introduced me to Flyway DB and I am now a fan. The introduction, documentation, and tutorial material is top-notch.

Installing Flyway on Linux

Flyway DB can be found here:

Although it has an API for integration, I specifically like the command-line utility version: https://flywaydb.org/getstarted/firststeps/commandline

Unzip the command-line tool version into your preferred program location. In my Linux VM, I decided on ~/bin:

image

and created a simlink to put flyway into the path:

$ ln -s ~/bin/flyway-4.2.0/flyway ~/bin/flyway

Now I can run it from any directory.

How Flyway works

Flyway scans the contents of a “migration scripts” folder using a file naming convention to understand which scripts belong to which specific version.

It then uses a special table in the target database called “schema_version” that contains metadata about the current version of the database.

Using Flyway

The basic syntax is

> flyway VERB

where VERB is one of:

  • migrate
  • clean
  • info
  • validate
  • baseline
  • repair

In our case, we need to:

  • “baseline” our database so that Flyway understands the current starting “version”;
  • write a DDL script to move the DB to the next version;
  • “migrate” our database instance to that version.

Setting up a working project directory

  • Create a working folder
  • copy the {install}/conf/flyway.conf file into the working directory, for project-specific overrides;
  • create a sub-folder called sql

The working directory I set up was:

/home/colin/Projects/flyway
/home/colin/Projects/flyway/sql

I copied the flyway.conf file, ready for local configuration.

Selecting the target DB

I’ve been working through the “MySQL Cookbook” tutorial, so I have a user and a database installed in the VM locally, called “cookbook”, with one table “limbs” already created.

Editing the .conf file:

flyway.url=jdbc:mysql://localhost:3306/cookbook
flyway.user=root
flyway.locations=filesystem:./sql

We could supply the password as well, but for interactive use it is safer to have flyway prompt for it. For automated processes, you’d want to put the password in the .conf file.

Note the syntax of specifying the location of the SQL migration scripts, with a “filesystem:” prefix.

Just for kicks, let’s run the “migrate” command:

$ flyway migrate
Flyway 4.2.0 by Boxfuse

Database password: ****
Database: jdbc:mysql://localhost:3306/cookbook (MySQL 5.7)
Successfully validated 0 migrations (execution time 00:00.003s)
ERROR: Found non-empty schema(s) `cookbook` without metadata table! Use baseline() or set baselineOnMigrate to true to initialize the
$

We see a couple of issues:

  • the target DB is missing the metadata table, and therefore Flyway doesn’t know what version it is;
  • we don’t have any upgrade scripts to process.

Baselining our target DB

We can update the .conf file to include information about the database. Let’s assume we are starting at version 5:

flyway.baselineVersion=5
flyway.baselineDescription=Baseline prior to Flyway

Now we can use the “baseline” command to create the metadata:

$ flyway baseline
Flyway 4.2.0 by Boxfuse

Database password: ****
Database: jdbc:mysql://localhost:3306/cookbook (MySQL 5.7)
Creating Metadata table: `cookbook`.`schema_version`
Successfully baselined schema with version: 5
$

Querying MySQL shows the table now exists:

mysql> show tables;
+--------------------+
| Tables_in_cookbook |
+--------------------+
| limbs |
| schema_version |
+--------------------+
2 rows in set (0.00 sec)

And the contents:

mysql> select * from schema_version;
+----------------+---------+--------------------------+----------+--------------------------+----------+--------------+--------------
| installed_rank | version | description | type | script | checksum | installed_by | installed_on
+----------------+---------+--------------------------+----------+--------------------------+----------+--------------+--------------
| 1 | 5 | Baseline prior to Flyway | BASELINE | Baseline prior to Flyway | NULL | root | 2017-06-12 14
+----------------+---------+--------------------------+----------+--------------------------+----------+--------------+--------------
1 row in set (0.00 sec)

We can use the “info” verb on the command-line to review the current version according to Flyway:

$ flyway info
Flyway 4.2.0 by Boxfuse

Database password: ****
Database: jdbc:mysql://localhost:3306/cookbook (MySQL 5.7)
+---------+--------------------------+---------------------+---------+
| Version | Description | Installed on | State |
+---------+--------------------------+---------------------+---------+
| 5 | Baseline prior to Flyway | 2017-06-12 14:23:41 | Baselin |
+---------+--------------------------+---------------------+---------+
$
Both schema and table name can be changed in the .conf, but it is probably better to leave it at default. For testing migrations on a freshly-built test database, there is a setting in the .conf that allows automatic default baselining if the schema table is not detected:

flyway.baselineOnMigrate=true

This can be very handy, along with specifying the DB user password, if security is not a priority.

Migrating the DB to a new version

Our current DB version is 5, but I’m going to create scripts for the versions either side of that, in order to see what Flyway does.

The script filenaming convention is documented here:

There are a number of possibilities including versioning scripts; repeatable scripts; and SQL callback scripts for invoking at various points during the process. For now, we’re just looking at versioning scripts.

Consider the following script files:

$ ls -l sql/*.sql
-rw-rw-r-- 1 colin colin 64 Jun 12 14:35 sql/V4__other_objects.sql
-rw-rw-r-- 1 colin colin 80 Jun 12 14:35 sql/V5__limbs.sql
-rw-rw-r-- 1 colin colin 62 Jun 12 14:36 sql/V6__test_table2.sql
$

Note: it may be tricky to remember that the name convention requires a double-underscore (“dunder”) between the version number and the file name!

Now, if we run the “info” verb:

Flyway 4.2.0 by Boxfuse
Database: jdbc:mysql://localhost:3306/cookbook (MySQL 5.7)

+---------+--------------------------+---------------------+---------+
| Version | Description | Installed on | State |
+---------+--------------------------+---------------------+---------+
| 4 | other objects | | <Baseln |
| 5 | Baseline prior to Flyway | 2017-06-12 14:23:41 | Success |
| 6 | test table2 | | Pending |
+---------+--------------------------+---------------------+---------+
$

Flyway detects this information from a) the script file naming convention, and b) the contents of the schema_version table in the target DB.

Questions:

  • Can we have more than one script belonging to a specific version?
  • If so, what is the execution sequence?
  • Can we have sub-versions (e.g. 5.1, 5.2 etc)?

The answer is that Flyway will throw an error if it detects two scripts associated with the same version number, so in fact you MUST use sub-version numbers for multiple scripts, like this:

V6_0__test_table2.sql
V6_1_1_test_table1.sql
V6_1_2__test_table3.sql

Of course, this now dictates the execution sequence:

$ flyway info
Flyway 4.2.0 by Boxfuse
Database: jdbc:mysql://localhost:3306/cookbook (MySQL 5.7)
+---------+--------------------------+---------------------+---------+
| Version | Description | Installed on | State |
+---------+--------------------------+---------------------+---------+
| 4 | other objects | | <Baseln |
| 5 | Baseline prior to Flyway | 2017-06-12 14:23:41 | Success |
| 6.0 | test table2 | | Pending |
| 6.1.1 | test table1 | | Pending |
| 6.1.2 | test table3 | | Pending |
+---------+--------------------------+---------------------+---------+

Now, let’s migrate!

$ flyway migrate
Flyway 4.2.0 by Boxfuse

Database: jdbc:mysql://localhost:3306/cookbook (MySQL 5.7)
Successfully validated 5 migrations (execution time 00:00.018s)
Current version of schema `cookbook`: 5
Migrating schema `cookbook` to version 6.0 - test table2
Migrating schema `cookbook` to version 6.1.1 - test table1
Migrating schema `cookbook` to version 6.1.2 - test table3
Successfully applied 3 migrations to schema `cookbook` (execution time 00:00.115s).
$

mysql> show tables;
+--------------------+
| Tables_in_cookbook |
+--------------------+
| limbs |
| schema_version |
| test1 |
| test2 |
| test3 |
+--------------------+
5 rows in set (0.00 sec)

mysql> select * from schema_version;
+----------------+---------+--------------------------+----------+--------------------------+-------------+--------
| installed_rank | version | description | type | script | checksum | install
+----------------+---------+--------------------------+----------+--------------------------+-------------+--------
| 1 | 5 | Baseline prior to Flyway | BASELINE | Baseline prior to Flyway | NULL | root
| 2 | 6.0 | test table2 | SQL | V6_0__test_table2.sql | 224077121 | root
| 3 | 6.1.1 | test table1 | SQL | V6_1_1__test_table1.sql | 669488585 | root
| 4 | 6.1.2 | test table3 | SQL | V6_1_2__test_table3.sql | -1574979834 | root
+----------------+---------+--------------------------+----------+--------------------------+-------------+--------
4 rows in set (0.00 sec)

And now:

$ flyway info
Flyway 4.2.0 by Boxfuse

Database: jdbc:mysql://localhost:3306/cookbook (MySQL 5.7)
+---------+--------------------------+---------------------+---------+
| Version | Description | Installed on | State |
+---------+--------------------------+---------------------+---------+
| 4 | other objects | | <Baseln |
| 5 | Baseline prior to Flyway | 2017-06-12 14:23:41 | Success |
| 6.0 | test table2 | 2017-06-12 15:01:22 | Success |
| 6.1.1 | test table1 | 2017-06-12 15:01:22 | Success |
| 6.1.2 | test table3 | 2017-06-12 15:01:22 | Success |
+---------+--------------------------+---------------------+---------+

It’s pretty cool!

Installing Oracle’s JDK in Ubuntu Linux

Just for my own notes, because I can never remember this stuff.

1. Check the architecture of your host:

colin@Mongpy:~$ uname -m
x86_64

2. Grab the appropriate download from Oracle’s web site:

image

My web browser puts it in the Downloads folder under home.

colin@Mongpy:~$ ls -l ~/Downloads
total 393356
drwxr-sr-x 7 colin colin 4096 Mar 31 12:21 eclipse-installer
-rw-rw-r-- 1 colin colin 185540433 May 25 13:19 jdk-8u131-linux-x64.tar.gz
-rw-rw-r-- 1 colin colin 21944320 Mar 29 14:18 mysql-workbench-community-6.3.9-1ubuntu16.10-amd64.deb
-rw-rw-r-- 1 colin colin 195297254 May 25 12:47 pycharm-community-2017.1.3.tar.gz

3. Open a terminal and get superuser access:

colin@Mongpy:~$ sudo su
[sudo] password for colin:
root@Mongpy:/home/colin#

4. Make a directory and expand the archive:

root@Mongpy:/home/colin# mkdir /opt/jdk
root@Mongpy:/home/colin# tar -zxf ./Downloads/jdk-8u131-linux-x64.tar.gz -C /opt/jdk
root@Mongpy:/home/colin# ls -l /opt/jdk
total 4
drwxr-xr-x 8 uucp 143 4096 Mar 15 01:35 jdk1.8.0_131

5. Review the current default JDK:

root@Mongpy:~# update-alternatives --display java
java - auto mode
link best version is /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java
link currently points to /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java
link java is /usr/bin/java
slave java.1.gz is /usr/share/man/man1/java.1.gz
/usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java - priority 1081
slave java.1.gz: /usr/lib/jvm/java-8-openjdk-amd64/jre/man/man1/java.1.gz

root@Mongpy:~# update-alternatives --display javac
javac - auto mode
link best version is /usr/lib/jvm/java-8-openjdk-amd64/bin/javac
link currently points to /usr/lib/jvm/java-8-openjdk-amd64/bin/javac
link javac is /usr/bin/javac
slave javac.1.gz is /usr/share/man/man1/javac.1.gz
/usr/lib/jvm/java-8-openjdk-amd64/bin/javac - priority 1081
slave javac.1.gz: /usr/lib/jvm/java-8-openjdk-amd64/man/man1/javac.1.gz

Note the current “priority” is 1081.

6. Set the Oracle version as the default JDK, using a higher priority, say 1090:

root@Mongpy:/home/colin# update-alternatives --install /usr/bin/java java /opt/jdk/jdk1.8.0_131/bin/java 1090

update-alternatives: using /opt/jdk/jdk1.8.0_131/bin/java to provide /usr/bin/java (java) in auto mode

root@Mongpy:/home/colin# update-alternatives --install /usr/bin/javac javac /opt/jdk/jdk1.8.0_131/bin/javac 1090

update-alternatives: using /opt/jdk/jdk1.8.0_131/bin/javac to provide /usr/bin/javac (javac) in auto mode

root@Mongpy:/home/colin# update-alternatives --display java
java - auto mode
link best version is /opt/jdk/jdk1.8.0_131/bin/java
link currently points to /opt/jdk/jdk1.8.0_131/bin/java
link java is /usr/bin/java
slave java.1.gz is /usr/share/man/man1/java.1.gz
/opt/jdk/jdk1.8.0_131/bin/java - priority 1090
/usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java - priority 1081
slave java.1.gz: /usr/lib/jvm/java-8-openjdk-amd64/jre/man/man1/java.1.gz

root@Mongpy:/home/colin# update-alternatives --display javac
javac - auto mode
link best version is /opt/jdk/jdk1.8.0_131/bin/javac
link currently points to /opt/jdk/jdk1.8.0_131/bin/javac
link javac is /usr/bin/javac
slave javac.1.gz is /usr/share/man/man1/javac.1.gz
/opt/jdk/jdk1.8.0_131/bin/javac - priority 1090
/usr/lib/jvm/java-8-openjdk-amd64/bin/javac - priority 1081
slave javac.1.gz: /usr/lib/jvm/java-8-openjdk-amd64/man/man1/javac.1.gz

7. Finally, testing:

colin@Mongpy:~$ java -version
java version "1.8.0_131"
Java(TM) SE Runtime Environment (build 1.8.0_131-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.131-b11, mixed mode)

Cool.

MySQL notes

The situation is that I have a MySQL database instance somewhere out on the network. And I’m trying to connect to it.

Logging in from the DB host

Plan:

  • Open a terminal window on the DB host, 192.168.1.130
  • Attempt to connect as the root db user
[root@zyxx01 ~]# mysql -u root
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

That didn’t work. This does, though:

[root@zyxx01 ~]# mysql -u root -p
Enter password: ****
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 171310
Server version: 5.5.32-log MySQL Community Server (GPL)

mysql>

So, don’t forget the -p option on the command-line. I guess that it tries first to connect without a password, which is a possible configuration for MySQL. And fails because it isn’t allowed in this instance.

Logging in from remote machine

My first attempt here didn’t work either, because “mysql” actually runs a batch file which expands into:

D:\>c:\progra~1\mysql\mysqls~1.5\bin\mysql.exe --defaults-file=c:\ProgramData\MySQL\mysqls~1.5\my.ini -uroot -p
Enter password: ********
ERROR 2003 (HY000): Can't connect to MySQL server on 'localhost' (10061)

Invoking the .exe directly avoids that interesting “defaults-file” thing:

D:\>c:\progra~1\mysql\mysqls~1.5\bin\mysql.exe -h 192.168.1.130 -u root -p
Enter password: ********
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 204151
Server version: 5.5.32-log MySQL Community Server (GPL)

Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>

Cool, we’re in. So now, let’s create a user:

mysql> create user 'abacab'@'%' identified by '****';
Query OK, 0 rows affected (0.00 sec)

mysql> grant all privileges on *.* to 'abacab'@'%' ;
Query OK, 0 rows affected (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

mysql>

Testing the user:

D:\>c:\progra~1\mysql\mysqls~1.5\bin\mysql.exe -h 192.168.1.130 -u abacab -p
Enter password: ***********
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 206648
Server version: 5.5.32-log MySQL Community Server (GPL)
...
mysql>

Success.

Finding the Data Dictionary in DB2

I’m not creating a special “DB2” category for this post 🙂

I’ve been looking for metadata, or some kind of data dictionary similar to those available in MS SQL Server or Oracle DB, to describe the tables and columns in a schema in DB2.

The closest match so far seems to be information in the SYSIBM library:

Specifically:

  • SQLCOLUMNS
  • SQLTABLES

Reference:

Selecting a timestamp AT TIME ZONE – a gotcha

So there’s this Oracle database instance in the midwest, in US/Central time zone.

So if I use PuTTY to open a terminal window on the host and open a SQL*Plus session, if I execute this statement I’ll get the following results:

SQL> select
max( CHANGE_TS ) as MAX_CHANGE,
max( CHANGE_TS at time zone 'US/Central' ) as MAX_CST_CHANGE
from tRetired_Mst;

MAX_CHANGE MAX_CST_CHANGE
-------------------------------- ---------------------------------------------
05-JAN-17 02.33.17.613000 PM 05-JAN-17 02.33.17.613000 PM US/CENTRAL

As expected, they are the same, because the local time zone of the session (terminal window) is the same as the DB, US/Central.

However:

If I run PL/SQL Developer on my Windows Laptop here in California, and connect to the same Oracle instance, then the results are different:

SQL> select
max( CHANGE_TS ) as MAX_CHANGE,
max( CHANGE_TS at time zone 'US/Central' ) as MAX_CST_CHANGE
from tRetired_Mst;

MAX_CHANGE MAX_CST_CHANGE
----------------------------- ----------------------------------------------
2017-01-05 14:33:17 05-JAN-17 04.33.17.613000 PM US/CENTRAL

Observe thatthe MAX_CST_CHANGE value is off by two hours! Because the timestamp value was evaluated as if it were in the local session time of my laptop, which is US/Pacific.

For code executing in PL/SQL packages in the database, this is probably not an issue… but if you are using this technique to convert values in ad-hoc SQL, you should be aware of this trap.

« Older posts Newer posts »

© 2020 More Than Four

Theme by Anders NorenUp ↑