[5.4] Fix bug related to sub select queries and extra select statements.

[ghost]

The sub select query must have only one selected column otherwise sql
will throw an error.

If a sub select function (e.g. withCount) is called with a model that
has select queries as a global scope this will cause the error.

The first column is the intended column for the sub select. Any global scope columns will be added after that. To avoid the error the columns array is reduced to just the first column.

This fix only applies to global scopes that use addSelect/selectRaw/withCount. If the select function is used it will replace all the columns and the sub select will return the first column in that select statement.

[laurencei]

Can you show a code example where this occurs? How would I replicate the error?

[ghost]

I'll give the example that lead me to find the bug.
Three models: User, Thread, Reply.
A user hasMany threads and replies.
A thread hasMany replies.
Lets say whenever you fetch the threads you want the reply count, so you add a global scope:

    protected static function boot()
    {
        parent::boot();

        static::addGlobalScope('replyCount', function (Builder $builder) {
            $builder->withCount('replies');
        });
    }

Now lets say you want to retrieve the users with their thread count:

    $users = User::withCount('threads')->get();

That code will then produce the following error:

SQLSTATE[HY000]: General error: 1 sub-select returns 2 columns - expected 1 (SQL: select "users".*, (select count(*), (select count(*) from "replies" where "threads"."id" = "replies"."thread_id") as "replies_count" from "threads" where "users"."id" = "threads"."user_id") as "threads_count" from "users")

I wrote a test which produces the invalid query in the commit.