Converts an entire database to utf-8. Handy when you forgot to set default_encoding etc. in my.cnf

convert_db_encoding.php

#/usr/bin/php
<?php
$mysqli = new mysqli('hostname', 'username', 'password');

$result = $mysqli->query(
	"SELECT `TABLE_SCHEMA`, `TABLE_NAME` FROM `information_schema`.`TABLES`
	WHERE
		`TABLE_COLLATION` != 'utf8_general_ci'
		AND `TABLE_SCHEMA` != 'mysql'
		AND `TABLE_SCHEMA` != 'information_schema'");
while($row = $result->fetch_array()) {
	$tableSchema = $row['TABLE_SCHEMA'];
	$tableName = $row['TABLE_NAME'];
	$mysqli->query(
	"ALTER TABLE `$tableSchema`.`$tableName`
	CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci") or die('Error: '.$mysqli->error);
	echo "Converted `$tableSchema`.`$tableName`\n";
}

$result = $mysqli->query(
	"SELECT `SCHEMA_NAME` FROM `information_schema`.`SCHEMATA`
	WHERE
		`DEFAULT_CHARACTER_SET_NAME` != 'utf8'
		AND `SCHEMA_NAME` != 'mysql'
		AND `SCHEMA_NAME` != 'information_schema'");
while($row = $result->fetch_array()) {
	$schemaName = $row['SCHEMA_NAME'];
	$mysqli->query("ALTER SCHEMA `$schemaName` CHARACTER SET = utf8") or die('Error: '.$mysqli->error);
	$mysqli->query("ALTER SCHEMA `$schemaName` COLLATE = utf8_general_ci") or die('Error: '.$mysqli->error);
	echo "Converted `$schemaName`\n";
}
?>
To avoid this problem in the future. Create the following files in /etc/mysql/conf.d
(debian specific setup, should work on other distributions as well)

## FILE: character_encoding.cnf

[client]
default-character-set = utf8

[mysqld]
character-set-server = utf8
collation-server     = utf8_general_ci

## FILE: default_storage_engine.cnf

[mysqld]
default-storage-engine = innodb

Better collation is utf8_unicode_ci. It support cyrillic letters.