Over time, some options have crept into the MySQL server which are comma separated lists of options. These include SQL_MODE, optimizer_switch, optimizer_trace and a few other variables.

Optimizer_switch is particularly problematic to work with as it contains many options and is hard to interpret. This is what you usually see when you examine optimizer_switch:

index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=on,mrr=on,mrr_cost_based=on,block_nested_loop=on,batched_key_access=off,materialization=on,semijoin=on,loosescan=on,firstmatch=on,subquery_materialization_cost_based=on,use_index_extensions=on

As you can see, seeing which option is on or off is rather difficult. You can use the REPLACE function to make this easier:

mysql> select replace(@@optimizer_switch, ',','\n')\G …

This is MySQL's Bad Idea #573 (after #384, which I've blogged about before) I've just had a terrible experience with a bug report from the jOOQ User Group, related to escaping of backslashes in string literals in MySQL. First, I thought to myself, whatever. SQL doesn't escape backslashes. The only escape character within a string … Continue reading MySQL Bad Idea #573 →

This article is part of a series. You might also like: 10 More Common Mistakes Java Developers Make when Writing SQLYet Another 10 Common Mistakes Java Developers Make When Writing SQL Java developers mix object-oriented thinking with imperative thinking, depending on their levels of: Skill (anyone can code imperatively)Dogma (some use the "Pattern-Pattern", i.e. the … Continue reading 10 Common Mistakes Java Developers Make when Writing SQL →

So far, I have been blogging about curious RDBMS caveats mostly related to Oracle and MySQL databases. Some examples: You never stop learning about Oracle features NOT IN vs. NOT EXISTS vs. LEFT JOIN / IS NULL: MySQL SQL incompatibilities: NOT IN and NULL values MySQL Bad Idea #384 But there are also other databases, … Continue reading 10 Things in SQL Server Which Don’t Work as Expected →

SQL tidbits are always valuable and highly searched for by newbies (as opposed to reading the SQL documentation). Sometimes we seasoned SQL developers take for granted little things like when a single- or multiple-character wildcard comparison works. It seems we know what newbies don’t. That you need a wildcard comparison operator not simply and equality comparison operator.

The question posed to me was, “Why doesn’t my wildcard comparison work?” Here’s a simplified example of their question.

SELECT 'Valid' AS "Test"
FROM    dual
WHERE  'Treat' = 'Tre_t'
OR     'Treet' = 'Tre_t';

Naturally, the answer is that the equality operator compares the strings based on their exact match (character sensitively in Oracle and character insensitively in MySQL). It needs to be rewritten by replacing the equals (=) comparison operator with the LIKE …

Join 8000 others and follow Sean Hull on twitter @hullsean. SQL is derided by many and for good reason. It’s key to scalability yet terribly difficult to write good code. Here’s a few quick tips to write tighter queries in MySQL 1. Get rid of those Subqueries! Subqueries are a standard part of SQL, unfortunately […]

The post 3 Simple Patterns for Tighter MySQL Code appeared first on Scalable Startups.

Join 7500 others and follow Sean Hull on twitter @hullsean.

There’s a lot of talk on the web about scalability. Making web applications scale is not easy. The modern web architecture has so many moving parts. How can we grapple with the underlying problem?

Also: Why Are MySQL DBAs So Hard to Find?

The LAMP stack scales well

The truth that is half right. True there are a lot of moving parts, and a lot to setup. The internet stack made up of Linux, Apache, MySQL & PHP. LAMP as it’s called, was built to be resilient, dynamic, and scalable. It’s essentially why Amazon works. Why what they’re doing is possible. Windows …

This is hypothetical.

What would happen if I did the following?

alter table mysql.user add unique key(User);

I’m tossing this out there for people to think about because I’ve always thought that MySQL’s authentication model is a nuisance:

MySQL considers both your host name and user name in identifying you because there is no reason to assume that a given user name belongs to the same person on all hosts. For example, the user joe who connects from office.example.com need not be the same person as the user joe who connects from home.example.com. MySQL handles this by enabling you to distinguish users on different hosts that happen to have the same name: You can grant one set of privileges for connections by joe from office.example.com, and a different set of privileges for connections by joe from home.example.com. ( …

I’ve posted slides for my Velocity talk on VividCortex’s blog. The talk explained how we use exponentially weighted moving statistics to generate a meta-metric of abnormality for the time-series metrics measured from MySQL. That’s kind of a mouthful. Maybe you had to be there :-)

Join 6100 others and follow Sean Hull on twitter @hullsean. Lots and lots of web applications need to page through information. From customer records, to the albums in your itunes collection. So as web developers and architects, it’s important that we do all this efficiently. Start by looking at how you’re fetching information from your [...]