相关疑难解决方法(0)

我有一张看起来像这个来电者'makerar'的桌子

 cname  | wmname |          avg           
--------+-------------+------------------------
 canada | zoro   |     2.0000000000000000
 spain  | luffy  | 1.00000000000000000000
 spain  | usopp  |     5.0000000000000000

我想为每个cname选择最大平均值.

SELECT cname, wmname, MAX(avg)  FROM makerar GROUP BY cname;

但我会收到一个错误,

ERROR:  column "makerar.wmname" must appear in the GROUP BY clause or be used in an   aggregate function 
LINE 1: SELECT cname, wmname, MAX(avg)  FROM makerar GROUP BY cname;

所以我这样做

SELECT cname, wmname, MAX(avg)  FROM makerar GROUP BY cname, wmname;

但这不会给出意图的结果,并显示下面的错误输出.

 cname  | wmname |          max           
--------+--------+------------------------
 canada …

我有一个db表说,persons在Postgres中由另一个有列名称的团队传下来,"first_Name".现在我正在尝试使用PG指令器在此列名称上查询此表.

select * from persons where first_Name="xyz";

它只是回归

错误:列"first_Name"不存在

不确定我是在做一些愚蠢的事情,还是我找不到这个问题的解决方法？

在安装了PostGis 2.2.0的Postgres 9.5数据库中,我有两个带有几何数据(点)的表,我想将一个表中的点分配给另一个表中的点,但我不想要分配两次.一旦分配了一个,就不应该将其分配给另一个.buildings.gidbuildings.gidpvanlagen.buildid

表定义

buildings:

CREATE TABLE public.buildings (
  gid numeric NOT NULL DEFAULT nextval('buildings_gid_seq'::regclass),
  osm_id character varying(11),
  name character varying(48),
  type character varying(16),
  geom geometry(MultiPolygon,4326),
  centroid geometry(Point,4326),
  gembez character varying(50),
  gemname character varying(50),
  krsbez character varying(50),
  krsname character varying(50),
  pv boolean,
  gr numeric,
  capac numeric,
  instdate date,
  pvid numeric,
  dist numeric,
  CONSTRAINT buildings_pkey PRIMARY KEY (gid)
);

CREATE INDEX build_centroid_gix
  ON public.buildings
  USING gist
  (st_transform(centroid, 31467));

CREATE INDEX buildings_geom_idx
  ON public.buildings
  USING …