>>> df = session.create_dataframe([1, -1, 1, -1, -1], schema=["a"])
>>> df.select(variance(col("a"))).collect()
[Row(VARIANCE("A")=Decimal('1.200000'))]
>>> df = session.create_dataframe([1, None, 2, 3, None, 5, 6], schema=["a"])
>>> df.select(variance(col("a"))).collect()
[Row(VARIANCE("A")=Decimal('4.300000'))]
>>> df = session.create_dataframe([None, None, None], schema=["a"])
>>> df.select(variance(col("a"))).collect()
[Row(VARIANCE("A")=None)]
>>> df = session.create_dataframe([42], schema=["a"])
>>> df.select(variance(col("a"))).collect()
[Row(VARIANCE("A")=None)]