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sql - Postgres : How to find nearest tsrange from timestamp outside of ranges?

转载 作者:行者123 更新时间:2023-11-29 12:10:01 26 4
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我正在为供应商提供的本地服务建模(在 Postgres 9.6.1/postGIS 2.3.1 中):

create table supplier (
id serial primary key,
name text not null check (char_length(title) < 280),
type service_type,
duration interval,
...
geo_position geography(POINT,4326)
...
);

每个供应商都有一个日历,其中包含可以预订的时间段:

create table timeslot (
id serial primary key,
supplier_id integer not null references supplier(id),
slot tstzrange not null,

constraint supplier_overlapping_timeslot_not_allowed
exclude using gist (supplier_id with =, slot with &&)
);

当客户想知道附近有哪些供应商可以在特定时间预订时,我创建了一个 View 和一个函数:

create view supplier_slots as
select
supplier.name, supplier.type, supplier.geo_position, supplier.duration, ...
timeslot.slot
from
supplier, timeslot
where
supplier.id = timeslot.supplier_id;


create function find_suppliers(wantedType service_type, near_latitude text, near_longitude text, at_time timestamptz)
returns setof supplier_slots as $$
declare
nearpoint geography;
begin
nearpoint := ST_GeographyFromText('SRID=4326;POINT(' || near_latitude || ' ' || near_longitude || ')');
return query
select * from supplier_slots
where type = wantedType
and tstzrange(at_time, at_time + duration) <@ slot
order by ST_Distance( nearpoint, geo_position )
limit 100;
end;
$$ language plpgsql;

所有这些都非常有效。

现在,对于在请求的时间没有可预订时间段的供应商,我想找到他们在请求的at_time 之前和之后的最近 可用时间段>,也按距离排序。

这让我有点头晕,我找不到任何合适的运算符来给我最近的 tsrange。

关于最聪明的方法有什么想法吗?

最佳答案

解决方案取决于您对所需内容的确切定义。

架构

我建议使用这些稍微调整过的表定义来简化任务、加强完整性并提高性能:

CREATE TABLE supplier (
supplier_id serial PRIMARY KEY,
supplier text NOT NULL CHECK (length(title) < 280),
type service_type,
duration interval,
geo_position geography(POINT,4326)
);

CREATE TABLE timeslot (
timeslot_id serial PRIMARY KEY,
supplier_id integer NOT NULL -- references supplier(id),
slot_a timestamptz NOT NULL,
slot_z timestamptz NOT NULL,
CONSTRAINT timeslot_range_valid CHECK (slot_a < slot_z)
CONSTRAINT timeslot_no_overlapping
EXCLUDE USING gist (supplier_id WITH =, tstzrange(slot_a, slot_z) WITH &&)
);

CREATE INDEX timeslot_slot_z ON timeslot (supplier_id, slot_z);
CREATE INDEX supplier_geo_position_gist ON supplier USING gist (geo_position);
  • 保存两个 timestamptzslot_aslot_z 而不是 tstzrangeslot - 并相应地调整约束。现在,这会将所有范围自动视为默认包含下限和不包含上限 - 这避免了角落案例错误/麻烦。

    附带好处:2 timestamptz 仅 16 个字节,而不是 tstzrange 的 25 个字节(32 个带填充)。

  • 您可能在 slot 上遇到的所有查询都将继续使用 tstzrange(slot_a, slot_z) 作为直接替换。

  • (supplier_id, slot_z) 上为手头的查询添加索引。
    以及关于 supplier.geo_position 的空间索引(您可能已经有了)。

    根据 type 中的数据分布,查询中常见类型的几个部分索引可能有助于提高性能:

    CREATE INDEX supplier_geo_type_foo_gist ON supplier USING gist (geo_position)
    WHERE supplier = 'foo'::service_type;

查询/函数

此查询找到 X 个提供正确 service_type 的最近供应商(示例中为 100 个),每个供应商都有 一个 最接近的匹配时间时隙(由到时隙开始的时间距离定义)。我将其与实际匹配的插槽相结合,这可能是也可能不是您需要的。

CREATE FUNCTION f_suppliers_nearby(_type service_type, _lat text, _lon text, at_time timestamptz)
RETURNS TABLE (supplier_id int
, name text
, duration interval
, geo_position geography(POINT,4326)
, distance float
, timeslot_id int
, slot_a timestamptz
, slot_z timestamptz
, time_dist interval
) AS
$func$
WITH sup_nearby AS ( -- find matching or later slot
SELECT s.id, s.name, s.duration, s.geo_position
, ST_Distance(ST_GeographyFromText('SRID=4326;POINT(' || _lat || ' ' || _lon || ')')
, geo_position) AS distance
, t.timeslot_id, t.slot_a, t.slot_z
, CASE WHEN t.slot_a IS NOT NULL
THEN GREATEST(t.slot_a - at_time, interval '0') END AS time_dist
FROM supplier s
LEFT JOIN LATERAL (
SELECT *
FROM timeslot
WHERE supplier_id = supplier_id
AND slot_z > at_time + s.duration -- excl. upper bound
ORDER BY slot_z
LIMIT 1
) t ON true
WHERE s.type = _type
ORDER BY s.distance
LIMIT 100
)
SELECT *
FROM (
SELECT DISTINCT ON (supplier_id) * -- 1 slot per supplier
FROM (
TABLE sup_nearby -- matching or later slot

UNION ALL -- earlier slot
SELECT s.id, s.name, s.duration, s.geo_position
, s.distance
, t.timeslot_id, t.slot_a, t.slot_z
, GREATEST(at_time - t.slot_a, interval '0') AS time_dist
FROM sup_nearby s
CROSS JOIN LATERAL ( -- this time CROSS JOIN!
SELECT *
FROM timeslot
WHERE supplier_id = s.supplier_id
AND slot_z <= at_time -- excl. upper bound
ORDER BY slot_z DESC
LIMIT 1
) t
WHERE s.time_dist IS DISTINCT FROM interval '0' -- exact matches are done
) sub
ORDER BY supplier_id, time_dist -- pick temporally closest slot per supplier
) sub
ORDER BY time_dist, distance; -- matches first, ordered by distance; then misses, ordered by time distance

$func$ LANGUAGE sql;

我没有使用您的 View supplier_slots 而是针对性能进行了优化。 View 可能仍然很方便。为了向后兼容,您可以包含 tstzrange(slot_a, slot_z) AS slot

查找 100 个最接近的供应商的基本查询是教科书“K 最近邻”问题。 GiST 索引对此很有效。相关:

附加任务(找到时间上最近的插槽)可以分为两个任务:找到下一个更高的行和下一个下一个更低的行。该解决方案的核心特征两个子查询ORDER BY slot_z LIMIT 1ORDER BY slot_z DESC LIMIT 1,这会导致两次非常快速的索引扫描。

我将第一个与查找实际匹配相结合,这是一个(我认为很聪明的)优化,但可能会分散实际解决方案的注意力。

关于sql - Postgres : How to find nearest tsrange from timestamp outside of ranges?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/41208541/

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