Search Results for: use key

Hijacking Innodb Foreign Keys

I guess I’m first to post in 2012 so Happy New Year all blog readers ! Now back to HardCore MySQL business – foreign Keys. MySQL supported Foreign Keys for Innodb for many years, yet rudimentary support initially added in MySQL 3.23.44 have not been improved in new releases as much as I’d like. We […]

Instrumentation and the cost of Foreign Keys

I occasionally get in to light arguments healthy discussions with students about whether or not to use Foreign Key constraints on InnoDB tables.  My standard response has always been: “it depends on how much of a tradeoff you are willing to make for performance. In some situations the cost can be considerable”. .. that’s when […]

Data mart or data warehouse?

This is part two in my six part series on business intelligence, with a focus on OLAP analysis. Part 1 – Intro to OLAP Identifying the differences between a data warehouse and a data mart. (this post) Introduction to MDX and the kind of SQL which a ROLAP tool must generate to answer those queries. […]

How (not) to find unused indexes

I’ve seen a few people link to an INFORMATION_SCHEMA query to be able to find any indexes that have low cardinality, in an effort to find out what indexes should be removed.  This method is flawed – here’s the first reason why:

The cardinality of status index is woeful, but provided that the application […]

3 ways MySQL uses indexes

I often see people confuse different ways MySQL can use indexing, getting wrong ideas on what query performance they should expect. There are 3 main ways how MySQL can use the indexes for query execution, which are not mutually exclusive, in fact some queries will use indexes for all 3 purposes listed here.