图在这里
https://wx3.sinaimg.cn/mw690/006yZBUAgy1g13okcrn8ij30u014078q.jpg

查询语句：
SELECT g.grid_no FROM city_grid g JOIN poi p ON g.city = '北京' and p.city = '北京' and g.grid_level = 1 and p.xm_type = '住宅' AND st_dwithin(g.center, p.location, 400) GROUP BY g.grid_no HAVING count(p.id) >= 3;

表结构如下

table city_grid 数据量 1600 万

address varchar(255),
box geography,
center geography,
city varchar(255),
grid_level integer,
grid_no integer

box gist 索引
center gist 索引
grid_no btree 索引

table poi 60 万

id serial not null constraint poi_pkey primary key,
address text,
city varchar(255),
district varchar(255),
location geography,
name varchar(255),
poi_id varchar(255),
type varchar(255),
type_code varchar(255),
xm_type varchar(255)

location gist 索引

@des 感谢关注，请移步 t/529929

终于可以了，期间打扰大家了