SQL中LAG、LEAD函数功能及用法

LAG(column, offset, default) OVER ([PARTITION BY] ORDER BY)

LEAD(column, offset, default) OVER ([PARTITION BY] ORDER BY)

SELECT 
    date,
    revenue,
    LAG(revenue, 1, 0) OVER (ORDER BY date) AS prev_revenue
FROM sales

SELECT 
    deptno,
    empname,
    salary,
    LAG(salary) OVER (PARTITION BY deptno ORDER BY hiredate) AS prev_salary
FROM emp

SELECT 
    date,
    revenue - LAG(revenue) OVER (ORDER BY date) AS daily_change
FROM sales

-- 写法一
select
customer_name
from 
（
select 
customer_name,
buy_date,
lag(buy_date,1) over(partition by customer_name order by buy_date) as next1_buy_date
lead(buy_date,1) over(partition by customer_name order by buy_date) as next1_buy_date
from
order_table
）
where
TIMESTAMPDIFF(day,buy_date,next1_buy_date) = -1
and
TIMESTAMPDIFF(day,buy_date,next2_buy_date) = 1;

-- 写法二
select
customer_name
from 
（
select 
customer_name,
buy_date,
lag(buy_date,1) over(partition by customer_name order by buy_date) as next1_buy_date
lag(buy_date,2) over(partition by customer_name order by buy_date) as next1_buy_date
from
order_table
）
where
TIMESTAMPDIFF(day,buy_date,next1_buy_date) = -1
and
TIMESTAMPDIFF(day,buy_date,next2_buy_date) = -2;