方差,var_pop,variance_pop

返回表达式的总体方差。从 v2.5.10 版本开始，此函数也可以用作窗口函数。

语法

VARIANCE(expr)

参数

expr: 表达式。如果它是一个表列，则必须计算为 TINYINT、SMALLINT、INT、BIGINT、LARGEINT、FLOAT、DOUBLE 或 DECIMAL。

返回值

返回 DOUBLE 值。

示例

MySQL > select var_pop(i_current_price), i_rec_start_date from item group by i_rec_start_date;
+--------------------------+------------------+
| var_pop(i_current_price) | i_rec_start_date |
+--------------------------+------------------+
|       314.96177792808226 | 1997-10-27       |
|       463.73633459357285 | NULL             |
|       302.02102643609123 | 1999-10-28       |
|        337.9318386924913 | 2000-10-27       |
|       333.80931439318346 | 2001-10-27       |
+--------------------------+------------------+

MySQL > select variance(i_current_price), i_rec_start_date from item group by i_rec_start_date;
+---------------------------+------------------+
| variance(i_current_price) | i_rec_start_date |
+---------------------------+------------------+
|        314.96177792808226 | 1997-10-27       |
|         463.7363345935729 | NULL             |
|        302.02102643609123 | 1999-10-28       |
|         337.9318386924912 | 2000-10-27       |
|        333.80931439318346 | 2001-10-27       |
+---------------------------+------------------+

关键词

VARIANCE,VAR_POP,VARIANCE_POP