[9.x] Fix issue with aggregates (withSum, etc.) for pivot columns on self-referencing many-to-many relations

[kayrunm]

An SQL error currently occurs when trying to run any withX aggregate functions on a column from a pivot table for a many-to-many relation that references the same table. The error that occurs is similar to the below:

Illuminate\Database\QueryException : SQLSTATE[HY000]: General error: 1 no such column: laravel_reserved_0.transaction_transaction.amount (SQL: select "transactions".*, (select sum("laravel_reserved_0"."transaction_transaction"."amount") from "transactions" as "laravel_reserved_0" inner join "transaction_transaction" on "laravel_reserved_0"."id" = "transaction_transaction"."allocated_to_id" where "transactions"."id" = "transaction_transaction"."allocated_from_id") as "total_allocated" from "transactions" limit 1)

The issue at hand is from lines 625–627 in QueriesRelationships:

$hashedColumn = $this->getQuery()->from === $relation->getQuery()->getQuery()->from
     ? "{$relation->getRelationCountHash(false)}.$column"
     : $column;

The condition in this ternary checks whether the current query references the same table as the relation's query, and if so, it prepends a "relationCountHash" which in the above error is "laravel_reserved_0". In a many-to-many relationship which references the same table, for example a "friends" relationship which links from a users table to the users table, this would return true and it would make referencing columns from a pivot table impossible in this situation.

My proposed fix for this is to move the above logic into a new method which checks for a period (.) in the $column, to see if the referenced column is on a different table to the original query. If this is the case, it just returns the $column, without the reserved table alias.

This shouldn't, to my knowledge, introduced any breaking changes with current versions as any columns passed in with a period are automatically escaped into "table_name"."column" syntax, rather than treated as a single column (e.g. "table_name.column".

[driesvints]

Please add a thorough explanation to your PR and don't link to an issue (see the pr template).

[kayrunm]

Apologies @driesvints, sorted now.

For more information on the issue, you can view the issue at #44285.