When you're spoiled with Oracle's fabulous query transformation capabilities and its really well-done cost-based optimiser, then you might forget how difficult SQL query tuning used to be in the "old days" or with those less sophisticated databases. Here's a really nice explanation of the various means of implementing an ANTI-JOIN in MySQL: http://explainextended.com/2009/09/18/not-in-vs-not-exists-vs-left-join-is-null-mysql/

I have seen a few posts on DBA.SE (where I answer a lot of questions) recommending the use of semi-synchronous replication in MySQL 5.5 over a WAN as a way to improve the reliability of replication. My gut reaction was that this is a very bad idea with even a tiny write load, but I wanted to test it out to confirm. Please note that I do not mean to disparage the author of those posts, a user whom I have great respect for.

What is semi-synchronous replication?

The short version is that one slave has to acknowledge receipt of the binary log event before the query returns. The slave doesn’t have to execute it before returning control so it’s still an asynchronous commit. …

The MySQL developer tools team announces the availability of version 5.2.41 of the MySQL Workbench GUI tool. This version has significant improvements in several parts of the tool and also includes the new Migration Wizard plugin.

The new Migration Wizard presents an easy to use GUI for migrating databases from third party products to MySQL. In this initial release, support for Microsoft SQL Server is included, in addition to other products that support ODBC, such as PostgreSQL.

Other improvements include:

• More than 100 bug fixes
• Code completion in the SQL Editor (beta)
• Better handling of schema synchronization in modeling

For a full list of issues fixed in this release, see  http://dev.mysql.com/doc/workbench/en/changes-5.2.x.html

Please get your copy from our Downloads …

If you haven’t checked into pt-online-schema-change yet, now’s a great time to sign up for my free webinar Thursday, July 19, 3-4 PM EDT. I’ll explain and demonstrate the tool, and walk you through everything you need to decide whether it’s right for you.

If you haven’t even heard about pt-online-schema-change yet, the short version is it lets you alter tables in MySQL with practically no downtime at all. This even works for really big tables that might take hours or days to alter — normally a blocking operation. In fact, 37Signals just wrote a blog post saying it has helped them achieve 99.99% uptime for their Basecamp …

One of the more notable success stories of the open source world is in the field of databases. A company with a strong commitment to open source has seen tremendous growth and success in the enterprise while contributing to a hugely respected open source code base. Who is that? Maybe your first thought was MySQL, now owned by Oracle. But unlike MySQL, this company is actually taking business away from Oracle so effectively that it's seen an 80 percent revenue growth in the last year.

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I was stunned when a SQL query raised an ERROR 1630 (42000) telling me the SUM function didn’t exist in MySQL 5.5.23. The fix was simple. The opening parenthesis of the SUM function must be on the same line as the SUM keyword without an intervening white space. Alternatively phrased, you can’t have a line return or white space between the SUM function name and the opening parenthesis of the call parameter list. The same rule doesn’t apply to the opening parenthesis of the FORMAT function and it seems to me that this parsing inconsistency is problematic.

Therefore, my surprise, observation, and complaint is that all functions don’t parse the same way, using the same rules. That is, unless you use specialized SQL_MODE settings. This assumption was borne out by Kolbe Kegel’s comment on this post, and there are 30 …

This post isn’t about NuoDB, although it was prompted by the phrase “100% uptime” that I’ve seen them use a few times. I want to suggest that people think slightly differently about uptime and availability.

The key to understanding uptime and thinking clearly about it, in my opinion, is to think instead about downtime. Uptime is the absence of downtime. Therefore, focus your attention on reducing downtime through a two-pronged approach. First, increase the mean time between failures (MTBF). Second, reduce the mean time to recovery (MTTR) when downtime happens. The techniques for achieving these goals are quite different; the second tends to be a technical solution, whereas the first usually requires a management solution.

Now, back to uptime. Is 100% uptime even possible? It depends on how you define it. Play funny with the definition, and you can draw a box around a period on your timeline where there was no downtime. …

I’ve been working on a data archival project over the last couple weeks and thought it would be interesting to discuss something a bit counter-intuitive. Absolutes are never true, but when getting rid of data, it’s usually more efficient to insert the data being kept into a new table rather than deleting the old data from the existing table.

Here is our example table from the IMDB database.

mysql> show create table title\G
*************************** 1. row ***************************
       Table: title
Create Table: CREATE TABLE `title` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `title` text NOT NULL,
  `imdb_index` varchar(12) DEFAULT NULL,
  `kind_id` int(11) NOT NULL,
  `production_year` int(11) DEFAULT NULL,
  `imdb_id` int(11) DEFAULT NULL,
  `phonetic_code` varchar(5) DEFAULT NULL,
  `episode_of_id` int(11) DEFAULT NULL,
  `season_nr` int(11) …

In my database class, students write solutions as group exercises against the Oracle 11g XE database and then they port the solution individually to the MySQL 5.5 database. One of the students copied over a query like the one below to MySQL (a query used to track the expected number of row returns).

SELECT   COUNT(*)
FROM    (SELECT   DISTINCT
                  k.kingdom_id
         ,        kki.kingdom_name
         ,        kki.population
         FROM     kingdom_knight_import kki LEFT JOIN kingdom k
         ON       kki.kingdom_name = k.kingdom_name
         AND      kki.population = k.population);

It got an error they didn’t understand:

ERROR 1248 (42000): Every derived TABLE must have its own alias

Providing a dt query alias fixes the problem in MySQL for the following query. The fact that it was just an alias was a revelation to the student. That’s because Oracle databases don’t require aliases …

Somebody wanted to understand why you can backquote a single wildcard operator (that’s the underscore _ character) in MySQL, but can’t in Oracle. The answer is you can in Oracle when you know that you required an additional clause.

While I prefer using regular expression resolution, the LIKE operator is convenient. Here’s an example of backquoting an underscore in MySQL, where it looks for any string with an underscore anywhere in the string:

SELECT   common_lookup_type
FROM     common_lookup
WHERE    common_lookup_type LIKE '%\_%';

You can gain the same behavior in Oracle by appending the ESCAPE '\' clause, like this:

SELECT   common_lookup_type
FROM     common_lookup
WHERE    common_lookup_type LIKE '%\_%' ESCAPE '\';

The ESCAPE '\' clause is one of those Oracle details that often gets lost. It only works when the SQL*Plus ESCAPE …