How to produce random rows from a table
A while ago, I were searching for a way to produce random rows from a table in MySQL. I found several solutions but none of them satisfied me. Of course, I could use a combined logic of MySQL and a...
View ArticleHow to retain comments in MySQL statements
There is a lot of buzz lately around retaining comments in MySQL’s logs and MySQL Stored procedures (Routines). When analyzing a MySQL query, it’s nice to have a comment inside the query (or procedure)...
View ArticleThe fading of Query Cache limitations
There is no question about the MySQL Query Cache greatness. The MySQL Query Cache feature started his way with some limitations. However, in time, there were a lot of improvements (fixing) for those...
View ArticleSelecting records from one table that dont have specific relationship in a...
Question: How can you select records from one table that doesn’t have a specific ID in a second, many-to-many table? In other words, imagine you have a questions table (A), categories table (B), and...
View ArticleConditional Joins in MySQL
One way to do a “Conditional Join” in MySQL is by using a “LEFT JOIN”. Create a “LEFT JOIN” for each condition and combine the results into one column using an “IF” statement by the “SELECT”...
View ArticleLimited SELECT count(*)
A SELECT statement with COUNT returns the number of rows retrieved by the SELECT statement (see mysql select count). For performance reasons, the desired result is to limit that count. Including a...
View ArticleMySQL User Defined Variables
When I have discovered MySQL User-defined variables at the first time, I didn’t pay much attention to them and didn’t realize their strength. At first, one can think that they are just one of the many...
View ArticleOptimizing the MySQL IN() Comparison Operations Which Include the Indexed Field
The MySQL IN() Comparison Operator is said to be very quick if all the values are constants (the values are then evaluated and sorted first, and the search is done using a binary search). However, what...
View ArticleThe battle between FORCE INDEX and the QUERY OPTIMIZER
Query Optimizer is a part of the server that takes a parsed SQL query and produces a query execution plan. MySQL Query Optimizer uses (as one of its parameters) the stored key distribution...
View ArticleA many to many relationship table – solving the exclude relation problem
A MySQL many to many relationship is a relationship that is multi-valued in both directions. Given that, how can you select rows that don’t have a specific relationship (the exclude relation problem)?...
View ArticleYou Must Have A Killer In Your System
Every system can have a slow query that randomly seems to emerge from nowhere. The main threat from these slow queries is that it can unexpectedly bring down your site. Even though the query is not...
View ArticleIf you copy a MyISAM table with PRIMARY key, don’t forget to order the rows...
In a case that you copy (INSERT INTO .. SELECT ..) a MyISAM table that have a PRIMARY key, it is much faster to insert the new rows in the primary key order: The insertion will be faster: because the...
View ArticleAs restoring a dump table into the MySQL master – you better get some sleep
Restoring a dump table into the MySQL master server can lead to serious replication delay. The massive inserts commands cause the Master and slaves to use most of their resources for replication. As a...
View ArticleMySQL Left Join
Even if you think you know everything about LEFT JOIN, I bet you will learn something or two in this post! The difference between the ON clause and the WHERE clause. A simple way to better understand a...
View Article
