Flattening

It is possible to flatten a GroupBy object into another instance of GroupBy with a single level of grouping sets.

$groupBy1 = new GroupBy(
    new RollUp(
        new Field('a'),
        new Field('b'),
    ),
);

$groupBy2 = new GroupBy(
    new GroupingSet(
        new FieldSet(),
        new FieldSet(
            new Field('a'),
        ),
        new FieldSet(
            new Field('a'),
            new Field('b'),
        ),
    ),
);

In the example above, $groupBy2 is the flattened version of $groupBy1. You can transform $groupBy1 into $groupBy2 using the flatten method.

$flattened = $groupBy1->flatten();

This is useful if you need to know if the GroupBy generates more than 4096 grouping sets, which is the limit of the database. Or, you can use it to split the query into multiple smaller queries.