CREATE TABLE city(
	country character varying(64),
	city character varying(64)
);

INSERT INTO city VALUES
('中国','台北'),
('中国','香港'),
('中国','上海'),
('日本','东京'),
('日本','大阪');

select country,string_agg(city,';' order by city desc) from city  group by country

select country,array_agg(city) from city  group by country

create table test_array(id int4[]);
INSERT INTO test_array(id) values(array[1,2,4]),(array[4,5,6]);

select array_agg(id) from test_array;

select array_length(id,1),id from test_array --显示一维度长度

select array_to_string(id,’ ‘) from test_array

select array_to_string(array_agg(id),’|') from test_array