mysql_collation.php fails if prefix is blank

0) Requirements 1. Developer is surely needed to test this. 2. MySQL 8 up and running, can use docker image easily. 3. Be able to run manual SQL commands against that MySQL 8 instance. 4. Ability to modify some PHP scripts. 1) Setting up 1 Set up a server with MySQL 8.0.2 or greater as the Moodle database. 2. Create the Moodle database using the utf8 character set and utf8_unicode_ci default collation, e.g.: CREATE DATABASE `mdl70181.test` DEFAULT CHARACTER SET utf8 COLLATE utf8_unicode_ci; CREATE USER 'mdl70181.test'@'localhost' IDENTIFIED BY 'yourpassword'; GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,CREATE TEMPORARY TABLES,DROP,INDEX,ALTER ON `mdl70181.test`.* TO 'mdl70181.test'@'localhost'; 3. Install Moodle pointing to the created database, either via the web interface or command line ensuring that the database table 'prefix' setting is set to blank (not 'mdl_'). 2) mysql_collation.php tests 1. After installation has completed, run the script to migrate to the utf8mb4 character set: php admin/cli/mysql_collation.php --collation=utf8mb4_unicode_ci 2. Verify that there aren't errors. Example last five lines tested with Moodle 3.9: ... ... workshopform_rubric_config - CONVERTED layout - NO CHANGE workshopform_rubric_levels - CONVERTED definition - NO CHANGE   Converted: 428, skipped: 1119, errors: 0 3) mysql_compressed_rows.php 0. Note: The following 2 steps are to force the system to detect the groups table to require fixing. 1. Connect to the MySQL from client and execute this SQL command: ALTER TABLE `groups` row_format = compact; COMMIT; 2. Edit the admin/cli/mysql_compressed_rows.ph y change the THREE occurrences of: if ($size <= $generator::ANTELOPE_MAX_ROW_SIZE) { to: if ($size <= $generator::ANTELOPE_MAX_ROW_SIZE && $table != 'groups') { 3. Run the CLI script: $ php admin/cli/mysql_compressed_rows.php --list 4. Verify that, apart from other tables... the "groups" one is shown as follows: groups Compact (needs fixing) 5. Run the CLI script: php admin/cli/mysql_compressed_rows.php --showsql 6. Verify that the suggested SQL to execute, include the groups table (with back-ticks) like this: ALTER TABLE `groups` ROW_FORMAT=Compressed; 7. Execute the the SQL shown in the previous step in the MySQL client. 8. Run again the cli script as it was in step 3. $ php admin/cli/mysql_compressed_rows.php --list 9. Verify that the groups table is listed, but it now shows the "Compressed" format and it does not say "(needs fixing)" anymore. Note, we cannot use the --fix option of the CLI, because it uses some MySQL parameters not available in MySQL 8 anymore. MDL-71512 has been created to fix that.