Upgrading an Existing MySQL Server

Fixes for bugs
No complex software such as MySQL can be free of bugs overtime, people discover unexpected behavior, or possible data corruption. As these problems come to light, they are fixed for the latest version. MySQL bugs are reported and analyzed at the http://bugs.mysql.com website. You can use this website to view the bug reports for your MySQL version and determine whether any are likely to affect your operations.
Fixes for security vulnerabilities
Security vulnerabilities are an especially dangerous class of bug by exploiting a vulnerability, an attacker could gain unauthorized access to data, or render your system unusable (cause a denial of service. If your server is connected to a network or otherwise accessible to people other than yourself, you need to take security issues very seriously.
Improved features
As software matures, new features are added to make some tasks easier or to improve efficiency. For example, MySQL 5.0 introduced support for views (virtual tables, stored procedures (predefined queries that clients can call, cursors (pointers to the result of database operations, and triggers (predefined operations that are carried out automatically before or after a row is inserted, deleted, or updated).
Similarly, subqueries (nested
SELECT
queries) were not possible in MySQL before version 4.1; neither were multiple concurrent character sets.
Some new features could greatly simplify your application, allowing you to reduce development time by simply upgrading your MySQL server. On a related note,
application software that you might want to use with your database server—for example, a free web portal system—might require you to have a minimum version of MySQL.
Newer versions of MySQL are generally backward-compatible with recent versions—
that is, older ways of doing things will continue to work. Anew server can work with old data, and even with older clients. For example, MySQL password management was improved inversion. The new server can correctly handle passwords stored in the old format, and, if it’s started with the old-passwords option, it can modify its behavior to cater to older clients, such as a web server that uses the old mechanism.
However, software is generally not upward-compatible—that is, you’re more likely to have difficulty if moving from a newer version of MySQL to an older version, especially if they are major versions apart (for example, moving from MySQL 5.0 to MySQL Its hard to find cases where downgrading is warranted.
You should assess your own needs and decide whether an upgrade is necessary or worthwhile if, for example, you have an online shopping application that’s running perfectly, you would only need to upgrade if you wanted to make changes that would be easier done with a newer MySQL version or if you learn of bugs that could affect the reliability or security of your site. Upgrading a MySQL server could require upgrades

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