sql - 获取有效的日期范围。最小值和最大值

Question

我需要按有效范围获取表格的值。目前，我按表格的列分组，并对年份进行了最小值和最大值；但这给了我这个例子的错误结果。我需要用语句 sql 或 pentaho 来解决它

示例数据:

year validity   Value1  Value2
2004               A     B
2006               A     C
2007               A     B
2008               A     B

SQL:

SELECT
    min(anio), max(anio), value1, value2
FROM tabla
GROUP BY
    value1, value2

错误结果:

year min    year max    Value1  Value2
2004        2008           A      B
2006        2006           A      C

预期结果:

year min    year max    Value1  Value2
2004        2004         A        B
2007        2008         A        B
2006        2006         A        C

请帮助解决这个问题。

Answer 1

您可以组合使用 LAG() 和 SUM() 窗口函数，根据您的逻辑将行分组。一旦分离，计算最小值和最大值就很简单了。

例如:

select
  min(year_validity) as year_min,
  max(year_validity) as year_max,
  min(value1) as value1,
  min(value2) as value2
from (
  select
    *,
    sum(init) over(order by year_validity) as grp
  from (
    select *,
    case when not ( (value1, value2) = (
      lag(value1) over(order by year_validity),
      lag(value2) over(order by year_validity)
    ) ) then 1 else 0 end as init
    from tabla
  ) x
) y
group by grp
order by value1, value2

结果:

year_min  year_max  value1  value2
--------  --------  ------  ------
2004      2004      A       B
2007      2008      A       B
2006      2006      A       C

为了记录，这个案例的数据脚本是:

create table tabla (
  year_validity int,
  value1 varchar(10),
  value2 varchar(10)
);

insert into tabla (year_validity, value1, value2) values (2004, 'A', 'B');
insert into tabla (year_validity, value1, value2) values (2006, 'A', 'C');
insert into tabla (year_validity, value1, value2) values (2007, 'A', 'B');
insert into tabla (year_validity, value1, value2) values (2008, 'A', 'B');