Raw SQL

query = """SELECT
        (SELECT COUNT(*) FROM user WHERE status = 'Admin')
        (SELECT COUNT(*) FROM user WHERE status = 'Member')
        (SELECT COUNT(*) FROM user WHERE status = 'Guest')
    """

>>> print database.raw(query).fetchone()
[2, 1, 0]

You can also use RAW SQL in select(), where(), group_by(), order_by()

folders = Folder.select(
        add_from='folder AS parent'
    ).where(
        'folder.left BETWEEN parent.left AND parent.right'
    ).group_by(
        'folder.id'
    ).order_by(
        'folder.left, folder.id'
    ).all()

You can check FyPress models for more examples: https://github.com/Fy-/FyPress/blob/master/fypress/folder/models.py