SilverStripe\ORM\DataList->columnUnique() is not unique

[elbroto]

Module version(s) affected

6.x, 5.x, 4.x

Description

\SilverStripe\CMS\Model\SiteTree::get()->columnUnique('ParentID');
The method name implies the result [0] but it returns [0, 0, 0, 0, 0].

How to reproduce

Make a clean installation, do /dev/build so that the five default pages are being build.

Call \SilverStripe\CMS\Model\SiteTree::get()->columnUnique('ParentID');

Possible Solution

Do array_unique() as its used in all other implementations of \SilverStripe\Model\List\SS_List->columnUnique()

Additional Context

No response

Validations

• Check that there isn't already an issue that reports the same bug
• Double check that your reproduction steps work in a fresh installation of silverstripe/installer (with any code examples you've provided)