📅 最后修改于: 2020-12-02 06:07:38 🧑 作者: Mango
本章详细说明了聚合和窗口功能。
集合函数从一组输入值产生单个结果。下表详细描述了聚合函数列表。
| S.No. | Function & Description |
|---|---|
| 1 | AVG(exp)
Averages a column of all records in a data source. |
| 2 | CORR(expression1, expression2)
Returns the coefficient of correlation between a set of number pairs. |
| 3 | COUNT()
Returns the number rows. |
| 4 | MAX(expression)
Returns the largest value of the selected column. |
| 5 | MIN(expression)
Returns the smallest value of the selected column. |
| 6 | SUM(expression)
Returns the sum of the given column. |
| 7 | LAST_VALUE(expression)
Returns the last value of the given column. |
Window函数在一组行上执行，并为查询中的每一行返回一个值。术语窗口具有该函数的行集的含义。
查询中的Window函数使用OVER()子句定义窗口。
OVER()子句具有以下功能-
下表详细描述了窗口功能。
| Function | Return type | Description |
|---|---|---|
| rank() | int | Returns rank of the current row with gaps. |
| row_num() | int | Returns the current row within its partition, counting from 1. |
| lead(value[, offset integer[, default any]]) | Same as input type | Returns value evaluated at the row that is offset rows after the current row within the partition. If there is no such row, default value will be returned. |
| lag(value[, offset integer[, default any]]) | Same as input type | Returns value evaluated at the row that is offset rows before the current row within the partition. |
| first_value(value) | Same as input type | Returns the first value of input rows. |
| last_value(value) | Same as input type | Returns the last value of input rows. |