What do multiple columns of a record being set to unique mean? Does the following mean that both columns or the combination of columns needs to be unique?

public function defineIndexes()
{
    return [
        ['columns' =&gt; ['productId', 'productTypeId'], 'unique' =&gt; true],
    ];
}
It means that no combination of those two columns can be the same in the table stated in the getTableName() of your record.