如何获取有关位置元素在表中的信息？

Question

我有查询：

Select * from mytable order by 'date' 

而且结果：

date | item_id | user_id | some_data 
------------------------------------------ 
2015-01-01 |  1 |  1 | null 
2015-01-01 |  1 |  1 | null 
2015-01-02 |  1 |  1 | null 
2015-01-03 |  1 |  1 | null 
2015-01-03 |  1 |  2 | null 
2015-01-04 |  1 |  1 | null 
2015-01-05 |  1 |  2 | null 

我想其中USER_ID = 2。在这个例子中是5怎么做第一排的位置？

Answer 1

select pos_overall 
from (
    select user_id, 
     row_number() over (order by "date") as pos_overall, 
     row_number() over (partition by user_id order by "date") as user_pos 
    from mytable 
) t 
where user_id = 2 
    and user_pos = 1 

Answer 2

您可以使用ROW_NUMBER（）函数与数日期，USER_ID的订单行，然后选择最小值：

select min(rn) 
from (
    select 
    user_id, row_number() over (order by date, user_id) as rn 
    from mytable 
) x 
where user_id = 2; 

如果ITEM_ID可以改变你可能要包括在派生表中的row_number函数的order by子句中。