Laravel and MySQL understanding Index and composite/compound index - mysql

Question

In Laravel (v 6.8) I have created below migration for the users table.
User Migration
public function up()
{
Schema::create('users', function (Blueprint $table) {
$table->bigIncrements('id');
$table->string('username')->unique()->index();
$table->string('email')->unique()->index();
$table->timestamp('email_verified_at')->nullable();
$table->string('password')->nullable();
$table->enum('role', ['super', 'admin', 'manager', 'subscriber', 'user'])->default('user');
$table->boolean('is_root')->default(FALSE);
$table->rememberToken();
$table->timestamps();
$table->unique(['username', 'email'], 'user_unique_credentials');
$table->index(['username', 'email'], 'user_index_columns');
});
}
Explaination
I know basics of index and how it works but I a having not so clear understanding about index on individual column and composite/compound index.
The App may have query by only username or email or I may have a query for both tables together. Therefore as you can see in my migration code, I have set index for each column as well as both columns using $this->index() that creates a compound index.
Question
I want to know if I have set all the indexes correctly or it is a bad idea to set up the way I did?
If it is not correct then may I know the correct way to do it?

Answer 1

#danblack thanks for your help.
Okay so trying with EXPLAINquery with various way setting up unique and index finally, I found the final version as below.
public function up()
{
Schema::create(
'users',
function (Blueprint $table) {
$table->bigIncrements('id');
$table->string('username')->unique();
$table->string('email')->unique();
$table->timestamp('email_verified_at')->nullable();
$table->string('password')->nullable();
$table->enum('role', ['super', 'admin', 'manager', 'subscriber', 'user'])->default('user');
$table->boolean('is_root')->default(FALSE);
$table->rememberToken();
$table->timestamps();
$table->unique(['username', 'email'], 'users_unique_credentials');
}
);
}
This way when we query on individual column, it will use own unique index. When we search with both columns with multiple WHERE clause it will use the compound unique index.