$table- unique laravel

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

    $table->foreign('user_id')->references('id')->on('users');
});Schema::table('tableName', function($table)
{
    $table->string('column-name')->unique(); //notice the parenthesis I added
});Schema::table('posts', function (Blueprint $table) {
    $table->unsignedBigInteger('user_id');

    $table->foreign('user_id')->references('id')->on('users');
});
OR
Schema::table('posts', function (Blueprint $table) {
    $table->foreignId('user_id')->constrained();
});