Hooray for Data Structures… Where Are They?

The Key-Value Pair is my favorite programming tool. Most SQL type databases lack this feature in it simplest form. Some would argue, “Well that’s because databases don’t need dah-blah-dee-blah-blah…” Well, if they don’t need it I don’t need to write this post. :p

How many times have you found yourself asking “Why isn’t there at least simple array support!?” When you don’t want the overhead of creating a table, or a temporary table, simple data structures really do come in handy (hint, hint, nudge, nudge to all the companies producing database software with stored routine support).

I’m not one to let an apparent lack of functionality ruin my day. Instead, I add it. I had a great computer science professor who said “You don’t need pointers to create a linked list.” Then he proved it. You can create, pretty much, any abstract data structure with …

We usually try to avoid subselects because sometimes they force the use of a temporary table and limits the use of indexes. But, when is good to use a subselect?

This example was tested over table a (1310723 rows), b, c and d ( 5 rows each) and with MySQL version 5.5 and 5.6.

Let’s suppose we have a query like this:

select a.name,sum(a.count) aSum,avg(a.position) aAVG,b.col1,c.col2,d.col3
from
a join
b on (a.bid = b.id) join
c on (a.cid = c.id) join
d on (a.did = d.id)
group by a.name,b.id,c.id,d.id

What will MySQL do? First it will take the entire data set – this means that will go through each row scanning the value of  “bid,” “cid” and “did” and then apply the join to each table. At this point it has the complete data set and then it will start to cluster it, executing the sum and the average functions.

Let’s analyze it step by step:

1. Scan each row of  table a which …

The MySQL developer tools team announces 6.3.4 as our GA release for MySQL Workbench 6.3.

For the full list of changes in this revision, visit
http://dev.mysql.com/doc/relnotes/workbench/en/changes-6-3.html

For discussion, join the MySQL Workbench Forums:
http://forums.mysql.com/index.php?151

Download MySQL Workbench 6.3.4 GA now, for Windows, Mac OS X 10.7+,
Oracle Linux 6 and 7, Fedora 21 and Fedora 22, Ubuntu 14.04, Ubuntu
14.10 and Ubuntu 15.04 or sources, from:

http://dev.mysql.com/downloads/tools/workbench/

Enjoy!

Changes in MySQL Workbench 6.3.4 (2015-06-15)

…

Why A Table of Dates?

I thought it would be nice to build on the numbers table with another very useful tool.

Dates are pretty important–especially if you are playing with data warehousing. Not only dates, but all the different properties and derived goodies contained within them. You really don’t need a dates table, unless you care about efficiency and getting to all the good stuff quickly. Perhaps I’ll showcase some of the “goodies” in later posts.

Sure, most databases have built-in functions to get everything you might want. But do you really want all the inefficiency that comes with calling functions and doing calculations over and over again? I hope not. I used the method in this article when I developed a SQL Server data warehouse for a company I worked for. It was adopted by our other SQL Server guru for all the date-sensitive stuff we did (which was a lot). It increased efficiency by leaps and …

Making The Numbers Table Useful

It’s not easy to find a solution to a very simple problem in MySQL: converting a comma separated list of values into rows. Oracle database users find gobs of tutorials on using REGEXP and CONNECT BY LEVEL to make this happen. MySQL doesn’t have that. So, use the numbers table from the previous post!

The transposing is made possible by (ab)using the SUBSTRING_INDEX function. I love this function. It is right up there with GROUP_CONCAT when mixing NULL and non-null strings.

I will be using comma separated values. You can use any delimiter character you like.

Bonus: This works with empty strings, strings with one value only, and empty delimiters (i.e. “my value,,previous is empty”). No extra code needed.

Making Magic Happen

SET @mycsv = …

Percona XtraDB Cluster (PXC) has become a popular option to provide high availability for MySQL servers. However many people are still having a hard time understanding what will happen to the cluster when one or several nodes leave the cluster (gracefully or ungracefully). This is what we will clarify in this post.

Nodes leaving gracefully

Let’s assume we have a 3-node cluster and all nodes have an equal weight, which is the default.

What happens if Node1 is gracefully stopped (service mysql stop)? When shutting down, Node1 will instruct the other nodes that it is leaving the cluster. We now have a 2-node cluster and the remaining members have 2/2 = 100% of the votes. The cluster keeps running normally.

What happens now if Node2 is gracefully stopped? Same thing, Node3 knows that Node2 is no longer part of the …

This Log Buffer Edition covers various blog posts from the last week regarding Oracle, SQL Server and MySQL.

Oracle:

• Merging Overlapping Date Ranges with MATCH_RECOGNIZE
• The latest version of Enterprise Manager, EM 12.1.0.5, has been announced!
• Kdump is the Linux kernel crash-dump mechanism. In the event of a server crash, Kdump creates a memory image (vmcore) that can help in determining the cause of the crash.
• …

Why You Care About Numbers

I have worked a bit with Oracle. As such, I hang out around Oracle developers. There seems to be a common complaint among our kind when it comes to MySQL–”There aren’t any sequences!”

It never really bothered me. I wasn’t always an Oracle guy, so I didn’t always have sequences. I’m the kind of person who likes to experiment and make things happen. It just so happens there is a nice tool to help with this perceived absence: the “numbers table.”

It is really easy to set up. And, regardless of your database background, I think you will grow to love your utility.

There are multiple ways to achieve the result you want. For me, the easiest way is to work with decimal numbers. Why? Because that’s how we think. That’s pretty much standard for humans. Yeah, I know. Geeks think hexadecimal. Let’s not go there.

Without further ado, here is how you can create …

Analyzing transactional data is becoming increasingly common, especially as the data sizes and complexity increase and transactional stores are no longer to keep pace with the ever-increasing storage. Although there are many techniques available for loading data, getting effective data in real-time into your data warehouse store is a more difficult problem. VMware Continuent provides

MySQL is getting native support for JSON.  This blog post will show you how to quickly get the MySQL server with these new features running on your Windows rig and how to write a small C# program in Visual Studio 2015 that stores a JSON document using the new native JSON data type.

Schema or Schemaless

The upcoming 5.7 version of MySQL introduces a ton of new features, some of which I am quite excited about—in particular the …