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我正在尝试优化复杂的 sql 查询，它将在每次地图绑定框更改时执行。我以为那INNER LATERAL JOIN会是最快的，但事实并非如此。有谁知道如何加快这个查询以及如何更好地利用LATERAL JOIN？

我做的最快的查询：

SELECT r0."id", r0."name" 
FROM "hiking"."routes" AS r0 
INNER JOIN "hiking"."hierarchy" AS h1 ON r0."id" = h1."parent" 
INNER JOIN (SELECT DISTINCT unnest(s0."rels") AS "rel" 
            FROM "hiking"."segments" AS s0 
            WHERE (ST_Intersects(s0."geom", ST_SetSrid(ST_MakeBox2D(ST_GeomFromText('POINT(1285982.015631 7217169.814674)', -1), ST_GeomFromText('POINT(2371999.313507 6454022.524275)', -1)), 3857)))) AS s2 ON TRUE 
WHERE (s2."rel" = h1."child");

计划时间：~0.605 ms 执行时间：~37.232 ms

实际上与上面相同，但使用LATERAL JOIN，它更慢是正确的吗？

SELECT r0."id", r0."name" 
FROM "hiking"."routes" AS r0 
INNER JOIN "hiking"."hierarchy" AS h1 ON r0."id" = h1."parent" 
INNER JOIN LATERAL (SELECT DISTINCT unnest(s0."rels") AS "rel" 
                    FROM "hiking"."segments" AS s0 
                    WHERE (ST_Intersects(s0."geom", ST_SetSrid(ST_MakeBox2D(ST_GeomFromText('POINT(1285982.015631 7217169.814674)', -1), ST_GeomFromText('POINT(2371999.313507 6454022.524275)', -1)), 3857)))) AS s2 ON TRUE 
WHERE (s2."rel" = h1."child");

计划时间：~1.353 ms 执行时间：~38.518 ms

子查询中子查询最慢的查询（这是我的第一个，所以我对其进行了一些改进）：

SELECT r0."id", r0."name" 
FROM "hiking"."routes" AS r0 
INNER JOIN (SELECT DISTINCT h0."parent" AS "parent" 
            FROM "hiking"."hierarchy" AS h0 
            INNER JOIN (SELECT DISTINCT unnest(s0."rels") AS "rel" 
                        FROM "hiking"."segments" AS s0 
                        WHERE (ST_Intersects(s0."geom", ST_SetSrid(ST_MakeBox2D(ST_GeomFromText('POINT(1285982.015631 7217169.814674)', -1), ST_GeomFromText('POINT(2371999.313507 6454022.524275)', -1)), 3857)))) AS s1 ON TRUE 
            WHERE (h0."child" = s1."rel")) AS s1 ON TRUE 
WHERE (r0."top" AND (r0."id" = s1."parent"));

计划时间：~1.017 ms 执行时间：~41.288 ms

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1 回答 1

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如果不了解您的数据库，很难重现您的查询逻辑，但我会尝试，所以请耐心等待：

SELECT r0."id", r0."name" 
FROM "hiking"."routes" AS r0 
INNER JOIN "hiking"."hierarchy" AS h1 ON r0."id" = h1."parent" 
WHERE 
  EXISTS (
    SELECT 1
    FROM "hiking"."segments" AS s0 
    WHERE (
      ST_Intersects(
        s0."geom",
        ST_SetSrid(ST_MakeBox2D(ST_GeomFromText('POINT(1285982.015631 7217169.814674)', -1), ST_GeomFromText('POINT(2371999.313507 6454022.524275)', -1)),
        3857)))
      AND array[h1."child"] <@ s0."rels");

有两点：

  1. EXISTS通过加入或NOT EXISTS有时比加入更快地过滤数据
  2. 您可以使用数组比较运算符，而不是取消嵌套数组字段以将其元素与某个值进行比较。拥有适当的 GIN 索引会更快（此处和此处的文档）。

以下是如何在数组上使用索引及其更快的简单示例：

create table foo(bar int[]);
insert into foo(bar) select array[1,2,3,x] from generate_series(1,1000000) as x;
create index idx on foo using gin (bar); // Note this
select * from foo where 666 in (select unnest(bar)); // 6936,345 ms on my HW
select * from foo where array[666] <@ bar; // 45,524 ms
于 2018-01-21T00:43:39.137 回答