Search Results for: mysql where clause

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.

Beware of MySQL Data Truncation

Here is nice gotcha which I’ve seen many times and which can cause just a minefield for many reasons. Lets say you had a system storing articles and you use article_id as unsigned int. As the time goes and you see you may get over 4 billions of articles you change the type for article_id […]

MySQL Optimizer team comments on TPC-H Results

Yesterday I had a chance to speak to Igor – head of MySQL optimizer team and Timur – both of them expressed concern with TPC-H run results I posted and notes about little gains in MySQL 6.0. Do not get this post wrong. I’m not saying MySQL 6.0 SubQuery optimizations are non existent or priorities […]

MySQL Performance – eliminating ORDER BY function

One of the first rules you would learn about MySQL Performance Optimization is to avoid using functions when comparing constants or order by. Ie use indexed_col=N is good. function(indexed_col)=N is bad because MySQL Typically will be unable to use index on the column even if function is very simple such as arithmetic operation. Same can […]