how to add foreign key in laravel migration after table has been created code example

Example 1: foreign key laravel migration

$table->foreign('column_name')->references('id')->on('table_name')->onDelete('cascade');

Example 2: create foreign key laravel migration

Schema::table('posts', function (Blueprint $table) {
    $table->unsignedBigInteger('user_id');

    $table->foreign('user_id')->references('id')->on('users');
});