[8.x] Fix duplicated columns on select

[gerardojbaez]

Description

Using $query->addSelect('something') multiple times introduces duplicated columns, causing SQLSTATE[42S21]: Column already exists: 1060 Duplicate column name 'something'.

Steps to reproduce

Execute the following query:

// accounts() is a many-to-many relation, with an intermediate Eloquent Model
App\User::find(1)->accounts()->groupBy('accounts.id')->select('accounts.*')->paginate();

The resulting problematic SQL query will be:

select count(*) as aggregate
from (select `accounts`.*,
             `accounts`.*,
             `membership`.`user_id`    as `pivot_user_id`,
             `membership`.`account_id` as `pivot_account_id`,
             `membership`.`id`         as `pivot_id`,
             `membership`.`created_at` as `pivot_created_at`,
             `membership`.`updated_at` as `pivot_updated_at`
      from `accounts`
               inner join `membership` on `accounts`.`id` = `membership`.`account_id`
      where `membership`.`user_id` = 1
      group by `accounts`.`id`) as `aggregate_table`

The second accounts.* is introduced by paginate() here:

framework/src/Illuminate/Database/Eloquent/Relations/HasManyThrough.php

Lines 434 to 447 in 361813c

	/**
	* Set the select clause for the relation query.
	*
	* @param array $columns
	* @return array
	*/
	protected function shouldSelect(array $columns = ['*'])
	{
	if ($columns == ['*']) {
	$columns = [$this->related->getTable().'.*'];
	}
	return array_merge($columns, [$this->getQualifiedFirstKeyName().' as laravel_through_key']);
	}

Related to #34096 #34097

[taylorotwell]

This can leave the keys out of numerical order which may have unexpected results in some situations. May want to review this.

[gerardojbaez]

You are right.

The issue is not a big deal and can be prevented on our end by passing an empty array to the paginate method: $query->paginate(15, []); this will prevent shouldSelect from adding the duplicated column.

Let me know should you want me to submit another improved solution.

Thanks!

[linaspasv]

Hm, calling $query->paginate(15, []) does not prevent duplicate column. Is there any solution for the problem?