php修改mysql数据库字符集

$conn = new mysqli("localhost", "username", "password", "database");
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

$sql = "ALTER DATABASE your_database_name CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci";
if ($conn->query($sql) === TRUE) {
    echo "数据库字符集设置成功";
} else {
    echo "Error: " . $conn->error;
}

$sql = "ALTER TABLE your_table_name CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci";
if ($conn->query($sql) === TRUE) {
    echo "表字符集设置成功";
} else {
    echo "Error: " . $conn->error;
}

$sql = "ALTER TABLE your_table_name MODIFY your_column_name VARCHAR(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci";
if ($conn->query($sql) === TRUE) {
    echo "字段字符集设置成功";
} else {
    echo "Error: " . $conn->error;
}