Tag: mysql 8.0.1

From MySQL 8.0.0 to MySQL 8.0.1 – or any other dev milestone

Disclaimer: This post is aimed to you, the curious developer, sys-admin, technologist, whatever-title-you-use. DO NOT run the following lines on production. Not even in a stable environment, do this if you don’t care about the outcome of the current data.

If you want to keep up with the newest MySQL developer milestones I have news for you: there is no upgrade available for milestone versions. The way to go is to remove old version and install new one, according to their website:

Upgrades between milestone releases (or from a milestone release to a GA release) are not supported. For example, upgrading from 8.0.0 to 8.0.1 is not supported, as neither are GA status releases.

So if you, like me, had the 8.0.0 version and want to test the 8.0.1 (alhtough 8.0.3 milestone is already in development) you need to do something like the following (tutorial based on Debian/Ubuntu servers).

Stop your service:

$ sudo service mysql stop

Download Oracle’s repository and install it, as of now this is the current version, you can get the new package here:

$ wget https://dev.mysql.com/get/mysql-apt-config_0.8.6-1_all.deb
$ sudo dpkg -i mysql-apt-config_0.8.6-1_all.deb

Clean your old install, you will lose all the data. Be careful, back up is on you!

$ sudo apt-get remove --purge mysql-server mysql-client mysql-common
$ sudo apt autoremove
$ sudo apt-get autoclean
$ sudo apt-get install mysql-server

This is the way to go to test the new features such as Descending Indexes and others. Remember, the new default encoding was changed from latin1 to utf8mb4.

Short feature list:

The complete list is available here.

What MySQL 8.0.1 means to you as a Developer

This post will be updated as soon more information comes along.

This developer version wasn’t released yet, when it does, use at your own risk.

Oracle released the development version of MySQL 8.0.0-dmr on September 12th of 2016. Since then, the team have been working on the 8.0.1 development milestone. You can find the partial change list here.

The objective here is try to explain how this will have any real world impact for you from 8.0.1. Please remember though, that any changes made to this version will not be final until the General Availability (date not currently set).

These topics are aimed at the Software Engineering side and not DBA and this is why Replication, for instance, is not covered here.


Charset and Collation

MySQL 8.0 was defined as to have utf8mb4 as the default CHARACTER SET and utf8mb4_general_ci as the default COLLATION. 8.0.1 will change the default COLLATION to utf8mb4_0900_ai_ci.

Let’s analyse the name utf8mb4_0900_ai_ci:

How does that impact you? It means that by default, new tables will have that collation and will be able to handle more characters than Basic Multilingual Plane (more emoji! 🤦🏼‍♀️), plus it will be accent and case insensitive. If you want case and accent sensitive you will need to use utf8mb4_0900_as_cs.

If you wish to know more about the reasons for utf8 now being utf8mb4 you should read this post on MySQL official blog: Sushi = Beer ?! An introduction of UTF8 support in MySQL 8.0

Language Specific Charsets

There are cases where language takes precedence over the default general collation. For this you will need to use, for example in the instance of German phone book order, utf8mb4_de_pb_0900_as_cs.


Descending Index

This particularly is one of my most desired features. Finally being implemented on this version, the ALTER TABLE ADD INDEX ix_column (column DESC) won’t be parsed as ASC anymore.

Since InnoDB uses BTREE indexes, when running a query that uses it in the case of single columns it doesn’t matter if the index is ASC or DESC. The index is used for DESC anyway.

However when working with multi-column indexes this will matter and having a descending index will actually increase your performance. Example:

A generic table users:

Field Type Null Key Default Extra
id int(10) unsigned NO PRI auto_increment
first_name varchar(127) NO
last_name varchar(128) NO
email varchar(255) NO
created_at timestamp NO CURRENT_TIMESTAMP
updated_at timestamp NO CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP

The following query will have better performance if run with DESC index on updated_at time column:

FROM `users`
ORDER BY updated_at DESC, first_name ASC
LIMIT 100;

For that we need the following index:

ADD INDEX `ix_updated_at_first_name`
(updated_at DESC, first_name ASC);

Before that, the query plan would do a full scan on the table and not use the index at all. After the index is created it searches on index, and not the table:

Before After
Before After

The query above is just a simplistic example and doesn’t filter anywhere the index, this is why it causes to do a full index scan.


I personally never made use for \N to indicate NULL in any query itself, but I have used it in CSV or TSV files.
This behaviour won’t be supported anymore.
This change won’t impact file import or export through LOAD DATA INFILE or SELECT ... INTO OUTFILE.


In-place operations

In MySQL 5.7 the Generated Columns feature was added. However ALTER TABLE in tables containing one would be a COPY operation (which is slower since it has to copy all data again of the table). Now it can be INPLACE as long as the column(s) being modified is not in a generated column. What this actually means is: the metadata for the column will be changed in real time, without the need to internally create a new table and copy data.



Two new functions are added to aggregate JSON values: JSON_ARRAYAGG() and JSON_OBJECTAGG().

JSON_ARRAYAGG() takes a column or expression as an argument and aggregates the result in a single JSON array.
With JSON_OBJECTAGG(id, col) you can use two columns which will be interpreted as key and value and returns a single JSON object.


Performance on JSON columns when used with ORDER BY was improved. Before MySQL would allocate 1K of memory to a sort key, making it fixed length. The extra padding was removed in this version.

Error Handling

The indexing of JSON fields is only possible through Generated Columns. If you tried to index a JSON field before, would get the following as an error:

JSON column '%s' cannot be used in key specification.

The error message has now been made clearer:

JSON column '%s' supports indexing only via generated columns on a specified JSON path.


More than 100 bugs were fixed on this version. It ranges from InnoDB through Replication and even compilation bugs. The list is too big to be tacked on to this article, but the complete (and yet partial) change list is available here.