sql - 如何将此子查询优化为联接？

Question

我注意到运行这个子查询

SELECT ST_Area(ST_Union(ST_Transform(ST_Intersection((SELECT poly1.the_geom from poly1 WHERE poly1.polygon_type='P'),poly2.the_geom),3857)))

AS area_of_P FROM poly1, poly2

比运行此连接慢得多

选择 ST_AREA（ST_Union（ST_Transform（ST_Intersection（poly1.the_geom，poly2.the_geom），3857）））

AS area_of_poly

从聚2

在 st_intersects(poly1.the_geom,poly2.the_geom) 上左连接 poly1

其中 poly2.polygon_type='P'

但是，我需要扩展第二个加入版本以返回更多列，每个列都计算给定多边形类型的面积，即

SELECT ST_Area(ST_Union(ST_Transform(ST_Intersection((SELECT poly1.the_geom from poly1 WHERE poly1.polygon_type='P'),poly2.the_geom),3857))) AS area_of_P,

ST_Area(ST_Union(ST_Transform(ST_Intersection((SELECT poly1.the_geom from poly1 WHERE poly1.polygon_type='S'),poly2.the_geom),3857))) AS area_of_S

来自 poly1, poly2

Answer 1

试试这个。

SELECT ST_AREA(ST_Union(ST_Transform(ST_Intersection(poly1.the_geom,poly2.the_geom),3857)))

AS area_of_poly

FROM poly2

LEFT JOIN poly1 on st_intersects(poly1.the_geom,poly2.the_geom)

WHERE poly2.polygon_type IN ( 'P', 'S' )

编辑：

SELECT ST_AREA(ST_Union(ST_Transform(ST_Intersection(ps.the_geom,poly2.the_geom),3857))) AS area_of_P,
       ST_AREA(ST_Union(ST_Transform(ST_Intersection(ss.the_geom,poly2.the_geom),3857))) AS area_of_S
FROM poly2
JOIN poly1 ps ON poly2.polygon_type = 'P' AND st_intersects(ps.the_geom,poly2.the_geom)
JOIN poly1 ss ON poly2.polygon_type = 'S' AND st_intersects(ss.the_geom,poly2.the_geom)