Foreach loop on a multi-dimensional PHP array returns complete wrong results [duplicate]

It doesn't look like anyone has mentioned this variation, so, for the benefit of future Googlers:

Combine the \PDO::FETCH_GROUP and \PDO::FETCH_COLUMN flags. This vastly simplified my SQL statement and returned the exact result set I wanted. It's fast, too.

$this->database->query('SELECT t.fk, t.id FROM my_table t ORDER BY t.fk ASC, t.id ASC') ->fetchAll(\PDO::FETCH_GROUP|\PDO::FETCH_COLUMN);

Where t.fk has a one-to-many relationship with t.id.

I didn't have to concern myself with a GROUP BY statement or MySQL's finicky handling of grouping on multiple fields. Best of all, I received results in the form of:

[ foreign_key_1 => [ 0 => 11111, 1 => 22222, 2 => 33333, ], foreign_key_2 => [ 0 => 44444, 1 => 55555, 2 => 66666, ], foreign_key_3 => [ 0 => 77777, 1 => 88888, 2 => 99999, ], ];

Rather than:

[ foreign_key_1 => [ 0 => [ id => 11111, ], 1 => [ id => 22222, ], 2 => [ id => 33333, ], ], foreign_key_2 => [ 0 => [ id => 44444, ], 1 => [ id => 55555, ], 2 => [ id => 66666, ], ], foreign_key_3 => [ 0 => [ id => 77777, ], 1 => [ id => 88888, ], 2 => [ id => 99999, ], ], ];

Hope it helps someone out there!

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For reference: https://phpdelusions.net/pdo/fetch_modes