POSTGIS，常用函数，实例

alter table public.dianping_qinzi add column geom geometry;

  单点  来生成 geom  用st_pointfromtext 函数:
update public.dianping_yule  set geom = st_pointfromtext('Point(' || lng || ' ' || lat || ')',4326 );

多点构成面（geom）用 ST_GeomFromText函数 ：
SELECT gaode, name ,ST_GeomFromText('Polygon(('||gaode||'))') as geom
from chengdu_boundary 
ORDER BY "name"

看有没有 4326  属性， ：
select st_srid(geom) from table

反解析 geom 出来 ：
st_astext
SELECT business_circle_name AS "名称",
st_astext(boundary)
from dt_crawler_businesscircle
where city_id='330100'
and business_circle_type='1'

参考网址 ：

https://www.w3cschool.cn/wqf_database/wqf_database-zsk92cz2.html

http://www.cnblogs.com/wuhenke/archive/2010/08/02/1790747.html

http://postgis.net/docs/ ** # 官方网址 #**

附送： 
建表语句 ：
CREATE TABLE public.dianping_yule
(
  shop_id character varying(255),
  name character varying(255),
  trade_area character varying(255),
  brand character varying(255),
  basetype text,
  tags text,
  subtype character varying(255),
  price double precision,
  rating integer,
  comment_count integer,
  strength double precision,
  environment double precision,
  service double precision,
  lng numeric,
  lat numeric,
  city character varying(255)
);