Question

我有一个sql表

id  item    date
A   apple   2017-09-17
A   banana  2017-08-10
A   orange  2017-10-01
B   banana  2015-06-17
B   apple   2014-06-18

如何编写SQL查询，以便对于每个id，我会根据日期获得最近的两个项目。例如：

id  recent second_recent   
a   orange  apple
b   banana  apple

Answer 1

您可以使用row_number()和条件聚合：

select id,
       max(case when seqnum = 1 then item end) as most_recent,
       max(case when seqnum = 2 then item end) as most_recent_but_one,
from (select t.*, 
            row_number() over (partition by id order by date desc) as seqnum
      from t
     ) t
group by id;

Answer 2

如上所述： SQL: Group by minimum value in one field while selecting distinct rows

您必须使用A组来获取分钟

SELECT mt.*,     
FROM MyTable mt INNER JOIN
    (
        SELECT item AS recent, MIN(date) MinDate, ID
        FROM MyTable
        GROUP BY ID
    ) t ON mt.ID = t.ID AND mt.date = t.MinDate

我认为您可以通过获取两个值而不是一个

来执行相同的操作

Answer 3

您可以使用数据透视表

SELECT first_column AS <first_column_alias>,
 [pivot_value1], [pivot_value2], ... [pivot_value_n]
 FROM
 (<source_table>) AS <source_table_alias>
 PIVOT
 (
 aggregate_function(<aggregate_column>)
 FOR <pivot_column> IN ([pivot_value1], [pivot_value2], ... [pivot_value_n])
 ) AS <pivot_table_alias>;

点击此处了解详情 Example

SQL查询以获取最近的项目

3 个答案: