我需要总结线性对象＆＃39;长度并按几年的间隔对它们进行分组。我有一个表存储我的对象，如下所示：
- gid serial NOT NULL,
- year INTEGER,
- the_geom geometry(MULTILINESTRING) ;
我需要这样的结果：
period | length
----------------+-----------
2005 - 2014 | 18.6
1995 - 2004 | 16.1
1985 - 1994 | 7.6
1975 - 1984 | 19.0
1965 - 1974 | 28.2
1945 - 1964 | 10.2
before 1945 | 0.1
我无法在网上找到如何执行此操作，除非使用不同的查询生成每一行并使用UNION ALL将它们合并在一起，这不太好...... < / p>
答案 0 :(得分：0)
假设以下内容得到了长度：
select year, length(the_geo) as len
from table
然后你的问题是找到长度相同的连续年份。我喜欢以下用于查找此类序列的技巧，假设您每年都有一个值：
select min(year) || '-' || max(year), len
from (select year, length(the_geo) as len,
(row_number() over (order by year) -
row_number() over (partition by length(the_geo) order by year)
) as grp
from table
) t
group by grp, len
order by 1;
答案 1 :(得分：0)
按整数除法的结果分组，有效地截断到除数的倍数 - 在你的情况下为10。按5切换以实现分区：
SELECT min(year)::text || ' - ' || max(year) AS period
, sum(length(the_geom)) AS "length"
FROM tbl
GROUP BY (year + 5) / 10
ORDER BY min(year) DESC;
/除法（整数除法截断结果）
答案 2 :(得分：0)
您需要一个判别函数，可以通过多种方式创建。为了您的目的，案例陈述只是票证，如：
select case
when t.year >= 2015 then '2015-present'
when t.year >= 2005 then '2005-2014'
when t.year >= 1995 then '1995-2004'
when t.year >= 1985 then '1985-1994'
when t.year >= 1975 then '1975-1984'
when t.year >= 1965 then '1965-1974'
when t.year >= 1955 then '1955-1964'
when t.year >= 1945 then '1945-1954'
when t.year < 1945 then 'before 1945'
else 'no year given'
end as period ,
sum( compute_length_from_geometry( t.geometry) ) as length
from some_table t
where .
.
.
group by case
when t.year >= 2015 then '2015-present'
when t.year >= 2005 then '2005-2014'
when t.year >= 1995 then '1995-2004'
when t.year >= 1985 then '1985-1994'
when t.year >= 1975 then '1975-1984'
when t.year >= 1965 then '1965-1974'
when t.year >= 1955 then '1955-1964'
when t.year >= 1945 then '1945-1954'
when t.year < 1945 then 'before 1945'
else 'no year given'
end as period
order by case
when t.year >= 2015 then 1
when t.year >= 2005 then 2
when t.year >= 1995 then 3
when t.year >= 1985 then 4
when t.year >= 1975 then 5
when t.year >= 1965 then 6
when t.year >= 1955 then 7
when t.year >= 1945 then 8
when t.year < 1945 then 9
else 10
end as period
你也可以考虑一个包括永久或临时的包围表，如：
create table report_period
(
period_id int not null ,
year_from int not null ,
year_thru int not null ,
period_description varchar(32) not null ,
primary key clustered ( period_id ) ,
unique nonclustered ( year_from , year_thru ) ,
)
insert report_period values ( 1 , 2015 , 9999 , '2015-present' )
insert report_period values ( 2 , 2005 , 2014 , '2005-2014' )
insert report_period values ( 3 , 1995 , 2004 , '1995-2004' )
insert report_period values ( 4 , 1985 , 1994 , '1985-1994' )
insert report_period values ( 5 , 1975 , 1984 , '1975-1984' )
insert report_period values ( 6 , 1965 , 1974 , '1965-1974' )
insert report_period values ( 7 , 1955 , 1964 , '1955-1964' )
insert report_period values ( 8 , 1945 , 1954 , '1945-1954' )
insert report_period values ( 9 , 0000 , 1944 , 'pre-1945' )
然后你的查询变得像
select p.period_description as period ,
sum( compute_length_from_geometry( t.geometry ) ) as length
from report_period p
join some_table t on t.year between p.year_from and p.year_thru
group by p.period_id ,
p.period_description
order by p.period_id
您甚至可以使用派生表来获得相同的效果
select p.period_description as period ,
sum( compute_length_from_geometry( t.geometry ) ) as length
from ( select 1 as period_id , 2015 as year_from , 9999 as year_thru , '2015-present' as period_description
UNION ALL select 2 as period_id , 2005 as year_from , 2014 as year_thru , '2005-2014' as period_description
UNION ALL select 3 as period_id , 1995 as year_from , 2004 as year_thru , '1995-2004' as period_description
...
) p
join some_table t on t.year between p.year_from and p.year_thru
group by p.period_id ,
p.period_description
order by p.period_id
或者，您也可以简单地进行整数除法，例如
period_id = ( 2014 - t.year ) / 10
这将为您提供域名
的句点标识符然后只需添加/减去适当的偏移量即可移动零点（或以年为单位更改计算偏移量）。
然而，这通常会否定列year上任何索引的使用，因为它现在是表达式。
答案 3 :(得分：0)
包围表report_period的解决方案非常出色，对我来说是最简单的。非常感谢尼古拉斯（以及所有人）！