How to convert MySQL collation from utf8mb4 to utf8

18 Comments / Web Development / By

Recently I faced a tough situation with one of my WordPress site at the time of exporting MySQL database. My development MySQL server supports utf8mb4 collation but the production MySQL server does not support that. So, I had to convert all the tables of the MySQL database from  utf8mb4 to utf8.  The actual task was conversion from utf8mb4_unicode_ci to utf8_general_ci

I tried to convert manually several times but it did not work. My question was what is the difference between utf8mb4 and utf8?

utf8mb4 (as well as standard UTF-8) can directly store any character specified by Unicode; the former is fixed size at 4 bytes per character whereas the latter is between 1 and 4 bytes per character.

utf8 can only store the first 65,536 codepoints, which will cover CJVK (Chinese, Japanese, Vietnam, Korean), and use 1 to 3 bytes per character.

So, the real process will be ALTER the database as well as each database table to change the CHARACTER SET.  Using a PHP script I made the conversion and it worked perfectly. This is the PHP script which will convert your MySQL database collation from utf8mb4_unicode_ci to utf8_general_ci instantly. 

<?php
$dbname = 'your-database-name';
mysql_connect('your-database-hostname', 'your-database-username', 'your-database-password');
mysql_query("ALTER DATABASE `$dbname` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci");
$result = mysql_query("SHOW TABLES FROM `$dbname`");
while($row = mysql_fetch_row($result)) {
$query = "ALTER TABLE {$dbname}.`{$row[0]}` CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci";
mysql_query($query);
$query = "ALTER TABLE {$dbname}.`{$row[0]}` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci";
mysql_query($query);
}
echo 'All the tables have been converted successfully';
?>
view raw dbconversion.php hosted with ❤ by GitHub
  1. Copy the above PHP script and paste in a file say, ‘dbconversion.php’.
  2. Now put this file in your server (development/production).
  3. Run this script from ‘yourdomain.com/dbconversion.php’.
  4. It’s all. It will convert everything and you will get a success message.

Note: If you are using WordPress website and you need to convert your database any time, make sure ‘utf8’ Charset will be defined in your ‘wp-config.php’ file as
define(‘DB_CHARSET’, ‘utf8’);

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18 thoughts on “How to convert MySQL collation from utf8mb4 to utf8”

  11. yoyo2030

    Hello!!

    How long does it take to convert the database? I got the success message but when I tried to upload the db to the new server still getting the error. My database is very big, like 200 M

    Reply
    1. Sanjay Bhowmick

      Generally you can not upload 200M file into any PHPMyAdmin. You have to edit your php.ini file and set the maximum values for
      memory_limit
      post_max_size
      upload_max_filesize
      and then restart your webserver.

      Reply
  13. grizzkN M Pattnaik

    I tried this script on my localhost installation and got a success message. But the table names in the database still showed ‘utf8mb4_unicode_520_ci’ and when I tried to migrate the website with Duplicator plugin I got database errors ‘unknown collation’, The migration failed. What else do I need to do for a successful migration. I do not know any programming but can handle some code editing.
    Hope you can help.
    Thanks.

    Reply
      1. N M Pattnaik

        Thanks for the offer. I have sent you the file. Still, it would be nice if you can please post the steps for doing it. I will be needing it more than once and others might too.

        Reply
      2. Wasif chowdhury

        i AM ALSO FACING THE SAME PROBLEM , AND I HAVE ALSO USED THE THE dbconversion.php code . BUT NOTHING HAPPENED.

        Reply

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