Sql on FromDual GmbH

SQL Query Tuning - Performance

oli.sennhauser@fromdual.com (Oli Sennhauser) — Mon, 05 Oct 2020 16:13:10 +0000

How could the following SQL queries be improved performance wise and otherwise and can you also explain why your change is more optimal?

Creating synthetic data sets for tuning SQL queries

oli.sennhauser@fromdual.com (Oli Sennhauser) — Fri, 02 Oct 2020 16:50:33 +0000

When it comes to SQL Query tuning with customers we often get the slow running SQL query and possibly, in good cases, also the table structure. But very often, for various reasons, we do not get the data.

MariaDB SQL Error Log Plugin

oli.sennhauser@fromdual.com (Oli Sennhauser) — Thu, 30 Jul 2020 12:26:18 +0000

When you are for too long in business you think you know already everything and you are getting lazy. This happened to me again a few weeks ago. A customer asked me about the SQL Error Log Plugin. First I though he was talking about the MariaDB Error Log or the General Query Log. But then I have learned that there is something “new” I did not know yet…

MariaDB/MySQL Stored Language Examples

oli.sennhauser@fromdual.com (Oli Sennhauser) — Thu, 19 Mar 2020 17:53:29 +0000

MariaDB/MySQL Stored Language is called SQL/PSM.
There are 4 different types of Stored Language: Stored Procedures, Stored Functions, Triggers and Events.

Enable General Query Log per Connection in MariaDB

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 10 Jul 2019 20:27:58 +0000

The General Query Log in MariaDB is a Log (file or table) that logs every statement sent from the Application to the MariaDB Database Server from the Connect Command to the Quit Command. A simple example you can find here:

Why you should take care of MySQL data types

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 25 May 2016 11:42:20 +0000

A customer reported last month that MySQL does a full table scan (FTS) if a query was filtered by a INT value on a VARCHAR column. First I told him that this is not true any more because MySQL has fixed this behaviour long time ago. He showed me that I was wrong:

Impact of column types on MySQL JOIN performance

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 11 Dec 2013 20:12:40 +0000

In our MySQL trainings and consulting engagements we tell our customers always to use the smallest possible data type to get better query performance. Especially for the JOIN columns. This advice is supported as well by the MySQL documentation in the chapter Optimizing Data Types:

Last login of MySQL database users

oli.sennhauser@fromdual.com (Oli Sennhauser) — Sat, 01 Dec 2012 10:05:50 +0000

MySQL hosting providers can easily loose the overview over their customers and which user or schema is still in use and which not.

Example 1

oli.sennhauser@fromdual.com (Oli Sennhauser) — Fri, 09 Dec 2011 10:07:51 +0000

CREATE TABLE `order` (
 id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY
, name VARCHAR(64) NOT NULL
) ENGINE = InnoDB;

INSERT INTO `order` VALUES
 (NULL, 'Test order 1')
, (NULL, 'Test order 2')
, (NULL, 'Test order 3');


CREATE TABLE pos (
 id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY
, order_id INT UNSIGNED NOT NULL
, name VARCHAR(64) NOT NULL
, amount SMALLINT NOT NULL
, price DECIMAL (6,2) NOT NULL
, status TINYINT NULL
) ENGINE = InnoDB;

INSERT INTO pos VALUES
 (null, 1, 'Schrauben', 50, 0.10, 0)
, (null, 1, 'Muttern', 50, 0.10, 0)
, (null, 2, 'Nägel', 1000, 0.05, 1);


CREATE TABLE pos_shadow LIKE pos;
ALTER TABLE pos_shadow ENGINE = MEMORY;
INSERT INTO pos_shadow SELECT * FROM pos;

delimiter //

CREATE TRIGGER upd BEFORE UPDATE ON pos
FOR EACH ROW
BEGIN
 UPDATE pos_shadow AS p
 JOIN `order` AS o ON o.id = p.order_id and o.id = NEW.order_id
 SET status = 1
 WHERE o.id = 1;
END;
//

delimiter ;

SELECT o.name, p.name, p.amount, p.price, (p.amount*p.price) AS total, p. status
 FROM `order` AS o
 JOIN pos_shadow AS p ON p.order_id = o.id
;

UPDATE pos AS p
 JOIN `order` AS o ON o.id = p.order_id AND o.id = 1
 SET p.status = 1, p.order_id = 1
 where o.id = 1;

SELECT o.name, p.name, p.amount, p.price, (p.amount*p.price) AS total, p. status
 FROM `order` AS o
 JOIN pos AS p on p.order_id = o.id
;

How good is MySQL INSERT TRIGGER performance

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 03 Aug 2011 17:08:36 +0000

Abstract: In this article we discuss how big is the performance impact of MySQL TRIGGERs compared to application side logging (with INSERT) into a MySQL table.

MySQL logon and logoff trigger for auditing

oli.sennhauser@fromdual.com (Oli Sennhauser) — Fri, 10 Dec 2010 23:23:51 +0000

A while ago I did some research about MySQL audit functionality and logon a and logoff triggers. MySQL and MariaDB provide a logon trigger in the form of the init_connect variable but no logoff trigger where most of the work for auditing would be done. When we would have a logoff trigger we could track the login and possibility some activity of a user and implement auditing functionality.

Materialized Views with MySQL

oli.sennhauser@fromdual.com (Oli Sennhauser) — Sat, 13 Mar 2010 13:55:05 +0000