LEAD
描述
LEAD() 是一个窗口函数，用于访问当前行之后的行数据，而无需进行自连接。它可以获取分区内当前行之后第 N 行的值。
语法
LEAD ( <expr> [ , <offset> [ , <default> ] ] )参数
| 参数 | 说明 |
|---|---|
| expr | 需要获取值的表达式 |
| offset | 向后偏移的行数。 |
| default | 当偏移超出窗口范围时返回的默认值。 |
返回值
返回与输入表达式相同的数据类型。
举例
计算每个销售员当前销售额与下一天销售额的差值：
select stock_symbol, closing_date, closing_price,
case
(lead(closing_price,1, 0)
over (partition by stock_symbol order by closing_date)-closing_price) > 0
when true then "higher"
when false then "flat or lower"
end as "trending"
from stock_ticker
order by closing_date;+--------------+---------------------+---------------+---------------+
| stock_symbol | closing_date | closing_price | trending |
| ------------ | ------------------- | ------------- | ------------- |
| JDR | 2014-09-13 00:00:00 | 12.86 | higher |
| JDR | 2014-09-14 00:00:00 | 12.89 | higher |
| JDR | 2014-09-15 00:00:00 | 12.94 | flat or lower |
| JDR | 2014-09-16 00:00:00 | 12.55 | higher |
| JDR | 2014-09-17 00:00:00 | 14.03 | higher |
| JDR | 2014-09-18 00:00:00 | 14.75 | flat or lower |
| JDR | 2014-09-19 00:00:00 | 13.98 | flat or lower |
+--------------+---------------------+---------------+---------------+