I’ve covered some strange default behavior around nulls in MySQL. There’s another nuance to this issue: you can still insert rows without specifying values for not null columns. MySQL will helpfully give you a default value (this is not really helpful – true help would be a quick failure with a descriptive error message). Let’s walk through this example.

mysql> Create Table NullTable (a Int Not Null, b Int Not Null);
Query OK, 0 rows affected (0.01 sec)

Here’s a table with two not null columns.

mysql> Insert Into NullTable (a) Values (1);
Query OK, 1 row affected, 1 warning (0.01 sec)

We can totally insert, even though we didn’t specify a value for b and b is not null.

mysql> Show Warnings;
+---------+------+----------------------------------------+
| Level   | Code | Message …

MySQL is the little engine that could. It powers sites like Facebook, YouTube, Twitter, and thousands of blogs, CMSes, and e-commerce sites. Its value to the world and to the development community could be measured in the hundreds of billions, and yet it’s free, and you can use it just by downloading it. Almost every programming language has drivers for it and it can run on so many operating systems and architectures, there’s really no limit on it.

Yet there’s a dark side. MySQL is full of gotchas and bugs, and it lacks features that sometimes call into question its status as a real database. The documentation is often open-ended and confusing, with gaps in key parts. If you want to run it, you have the option of using it on Linux, Mac, Solaris, or Windows and every hosting company or provider like Amazon AWS has their own managed service, each with its own quirks and limitations. The user community has also produced thousands of …

It's again that time of the year. Analysts are spending oceans of words to predict the future, companies are making plans for the next year and people are resting and enjoying the break with their families. To me, this is the perfect time to reflect on my choices, the direction I'm headed to and consider if I still love what I do.

At the beginning of the year I decided to join MongoDB (formerly 10gen). The more I think about it, the more I realize I've been wrong. Yes, it's been the worst decision in my life not to join MongoDB when I was first offered the opportunity years ago. At that time an insightful friend asked me to consider the opportunity. At that time I didn't see what I see today.

I didn't see the …

It's again that time of the year. Analysts are spending oceans of words to predict the future, companies are making plans for the next year and people are resting and enjoying the break with their families. To me, this is the perfect time to reflect on my choices, the direction I'm headed to and consider if I still love what I do.

At the beginning of the year I decided to join MongoDB (formerly 10gen). The more I think about it, the more I realize I've been wrong. Yes, it's been the worst decision in my life not to join MongoDB when I was first offered the opportunity years ago. At that time an insightful friend asked me to consider the opportunity. At that time I didn't see what I see today.

I didn't see the …

In my last post, a tale of two MySQL upgrades, a few folks asked if I would outline the process we used to upgrade, and what kind of downtime we had.

Well, the processes were different for each upgrade, so I will tackle them in separate blog posts. The first step was to upgrade all our MySQL 5.1 machines to MariaDB 5.5. As mentioned in the previous post, MariaDBs superior performance for subqueries is why we switched and we switched back to MySQL for 5.6 to take full advantage of the performance_schema.

It is not difficult to blog about our procedure, as we have documentation on each process. My first tip would be to do that in your own environment. This also enables other folks to help, even if they are sysadmins and not normally DBAs. You may notice the steps contain items that might be obvious to someone who has done maintenance before we try to …

At the beginning of 2013, Mozillas MySQL databases were a mix of MySQL 5.0, Perconas patched MySQL 5.1, Perconas patched MySQL 5.5 and MariaDB 5.5. MySQL 5.1 was released in November 2008 so at the beginning of the year, we still had databases with no new major features in 4 years. Currently we have almost all our databases at Oracle’s MySQL 5.6 — the only stragglers are our cluster running TokuDB and a few machines that are no longer in use. Heres a graph showing the state of our machines you can see that in the first half of the year we concentrated on upgrading our 5.0 and 5.1 servers to 5.5, and then in the second half of the year we upgraded everything to MySQL 5.6 (click on the image to get the .png file):

…

Within MySQL, there’s a piece called a storage engine that reads and writes to disk on your behalf when you execute a query. It controls the way that your data is stored on disk. With MySQL, you can change what storage engine you use, which is helpful since every engine has different advantages and downsides, and you can select which engine to use based on your workload. There are two main engines: MyISAM and InnoDB. MyISAM was the default engine before MySQL 5.5 and it’s been there since the beginning. It’s also not crash-proof, it doesn’t have foreign keys, and it’s not transactional. InnoDB, on the other hand, has all these features.

What happens if you use MyISAM

No Safety Belt

Grooveshark (a popular music site) in …

I recently came across an issue trying to connect to a MySQL server using the mysql client. It appeared as through the connection was hanging.

A subsequent connection using the -A option highlighted the problem with the previous connection stuck in the state “Waiting for table metadata lock”.

mysql> SHOW PROCESSLISTG
*************************** 1. row ***************************
     Id: 37
   User: root
   Host: localhost
     db: tmp
Command: Query
   Time: 90
  State: preparing
   Info: create table missing as select id from AK where id not in (select id ..
*************************** 2. row ***************************
     Id: 38
   User: root
   Host: localhost
     db: tmp
Command: Field List
   Time: 50
  State: Waiting for table metadata lock
   Info:
*************************** 3. row ***************************
     Id: 39
   User: root
   Host: localhost
     db: tmp
Command: Query
   Time: 0
  State: init
   Info: show processlist …

Yesterday we had our third Madrid MySQL users group meeting. That was quite interesting.  Thanks go to Juan for his presentation.

We plan the next meeting on January 16th after the New Year is out of the way. If you are interested in MySQL and happen to be in Madrid please consider coming to see us.

More information about the next meeting can be found on the group’s web page. Note: The meeting will be in Spanish. I look forward to seeing you.

Next week the US celebrates Thanksgiving Day. For those that are American or live here, this is a significant event. Three different experiences recently have lead me to write this request for ALL MySQL community members to give thanks to those that have contributed to the MySQL ecosystem. I have made a commitment to myself, and I would like to challenge others to write one book review per week in December, that’s 4 book reviews to the MySQL books that I have on my bookshelf that have made an impact in some way. I ask others to give it a go too.

It only takes a few minutes to pen a comment on Amazon, or a publishers site, but to authors it means so much more. I can only speak for myself, but any comment; good, bad or ugly; helps to know you are out there and you took the time to acknowledge somebody’s work of art (in this case a publication).

I only have to look at my bookshelf and I find the following MySQL books (in …