VAR_POP [analytic]
返回 窗口内组中非 null 数字集（忽略 null 值）的统计总体方差。结果的计算方法为 expression 与 expression 均值之差的平方和除以剩余行数：
(SUM( expression * expression ) - SUM( expression ) * SUM( expression ) / COUNT( expression )) / COUNT( expression )
行为类型
不可变语法
VAR_POP ( expression ) OVER (
[ window-partition-clause ]
[ window-order-clause ]
[ window-frame-clause ] )
参数
- 表达式
- 任何
NUMERIC数据类型或可隐式转换为数字数据类型的任何非数字数据类型。函数返回的数据类型与参数的数字数据类型相同 OVER()- 请参阅分析函数
示例
下述示例计算 2007 年 1 月商店销售事实表的累计总体方差：
=> SELECT date_ordered,
VAR_POP(SUM(total_order_cost))
OVER (ORDER BY date_ordered) "var_pop"
FROM store.store_orders_fact s
WHERE date_ordered BETWEEN '2007-01-01' AND '2007-01-31'
GROUP BY s.date_ordered;
date_ordered | var_pop
--------------+------------------
2007-01-01 | 0
2007-01-02 | 89870400
2007-01-03 | 3470302472
2007-01-04 | 4466755450.6875
2007-01-05 | 3816904780.80078
2007-01-06 | 25438212385.25
2007-01-07 | 22168747513.1016
2007-01-08 | 23445191012.7344
2007-01-09 | 39292879603.1113
2007-01-10 | 48080574326.9609
(10 rows)