In several RDBMS databases, including MySQL, subqueries are often one of the causes for performance issues. Therefore, we have an incentive to avoid them whenever we can and to find alternative ways to implement our requirements.

One of the most popular uses for subselects in SQL is when one needs to fetch the first, last, maximum or minimum row for each group in a table. For example, how would you implement an SQL query that should fetch the employees with the maximum salary for each department from the employees table? Actually, fetching the salary itself is pretty easy, but it becomes more complicated when you want to fetch the employee name (the row data) along with the maximum salary.

Let’s look at the table:

For the impatient:

# echo -e "deb http://repo.mysql.com/apt/debian/ stretch mysql-5.7\ndeb-src http://repo.mysql.com/apt/debian/ stretch mysql-5.7" > /etc/apt/sources.list.d/mysql.list
# wget -O /tmp/RPM-GPG-KEY-mysql https://repo.mysql.com/RPM-GPG-KEY-mysql
# apt-key add /tmp/RPM-GPG-KEY-mysql
# apt update
# apt install mysql-server

In the latest stable version of Debian, if you ask to install mysql-server, you now get installed mariadb automatically, with no (evident) way of installing Oracle’s MySQL. Any major version upgrade has to be done carefully (not only for MariaDB, but also for MySQL and Postgres), and I bet that a MySQL 5.5 to MariaDB 10.1 will cause a huge confusion. Not only it will fail user expectations, I think this will cause large issues now that MariaDB has chosen to become a “hard” fork, and become incompatible in many ways with MySQL. Not only the server upgrade will cause user struggle, the connector is …

Last Thursday, I was introducing MySQL Document Store in Ghent, BE at Percona University.

I was explaining how great is this technology and how MySQL can replace your NoSQL database but still provides you all the benefits from a RDBMS.

This is the full presentation:

Introduction to MySQL Document Store from Frederic Descamps

Then somebody came with a nice question. Let me put first some context:

• we will create a collection to add people in it
• we will create a virtual column on the age
• we will index that column
• we will query and add records to that collection

Collection creation and add some users

mysql-js> schema = …

以前の記事では、MySQL 8.0.1で導入された新しい 日本語のutf8bm4のCollation(文字照合順)について ご紹介しました。このcollation (utf8mb4_ja_0900_as_cs) は、CLDR 30で定義されたアクセント記号(清音濁音半濁音)ならびに大文字小文字(拗音促音など)を判別する実装となっています。

今日ご紹介するのはひらがなカタカナを判別できる新しい「かなセンシティブ」なCollation utf8mb4_ja_0900_as_cs_ksです。 …

MySQL 8.0.1では、utf8mb4の大文字小文字およびアクセント記号付きの文字を判別するas_cs collationに加えて、日本語用のCollation(文字照合順)を追加しました。

utf8mb4_ja_0900_as_csについて

日本語に関する文字照合およびソートのルールは複雑です。日本語ではひらがな、カタカナ、漢字、アルファベット(ラテン文字)を混在させて利用しています。さらに、全角と半角が存在する文字もあります。では、‘あ’, ‘ア’, ‘a’, ‘ｱ’はどのようにソートされるのでしょうか？

Unicode照合アルゴリズム(UCA / Unicode Collation …

If you ever tried to backup MySQL 5.7 with Percona Xtrabackup that comes in percona-xtrabackup package most likely you got error message like this: [crayon-5ba957f33e1f1811481611/] This happens because percona-xtrabackup actually installs version 2.3 that doesn’t support MySQL 5.7. To take copies from MySQL 5.7 you need to use Percona XtraBackup version 2.4 and higher. Starting from […]

The post How to Backup MySQL 5.7 appeared first on TwinDB.

In this blog post, we’ll look at how ClickHouse performs in a general analytical workload using the star schema benchmark test.

We have mentioned ClickHouse in some recent posts (ClickHouse: New Open Source Columnar Database, Column Store Database Benchmarks: MariaDB ColumnStore vs. Clickhouse vs. Apache Spark), where it showed excellent results. ClickHouse by itself seems to be event-oriented RDBMS, as its name suggests (clicks). Its primary purpose, using Yandex Metrica (the system similar to Google Analytics), also points to an event-based nature. We also can see there is …

Debian logo by Software in the Public Interest, Inc. (CC-BY-SA) MySQL and Debian 9 “Stretch” Debian 9 (“Stretch”) was released on June 17, and we congratulate the Debian community on another iteration of a central Linux distro. Now, the Debian release team some time ago decided not to ship MySQL as part of the distro, instead replacing it […]

We’ll show you How to Install LAMP on Ubuntu 16.04. LAMP (Linux, Apache, MySQL, PHP) is a combination of open ...

Read moreHow to Install LAMP on Ubuntu 16.04

The post How to Install LAMP on Ubuntu 16.04 appeared first on RoseHosting.

Often databases contain data that needs to be proven as valid and authentic. We want to ensure that a known person or other sender (e.g. a trusted app) of the information can’t deny content, nor that the content can change without that person (senders) consent.…