如何在Postgresql数据库中显示航空公司是否从所有机场出发?
我的数据库中有3个表:如何在Postgresql数据库中显示航空公司是否从所有机场出发?,sql,postgresql,Sql,Postgresql,我的数据库中有3个表: CREATE TABLE airlines ( airline_name VARCHAR NOT NULL PRIMARY KEY ); CREATE TABLE airport ( code VARCHAR UNIQUE NOT NULL PRIMARY KEY, name VARCHAR NOT NULL, category VARCHAR NOT NULL, city VARCHAR NOT NULL ); CREATE
CREATE TABLE airlines (
airline_name VARCHAR NOT NULL PRIMARY KEY
);
CREATE TABLE airport (
code VARCHAR UNIQUE NOT NULL PRIMARY KEY,
name VARCHAR NOT NULL,
category VARCHAR NOT NULL,
city VARCHAR NOT NULL
);
CREATE TABLE volo (
code VARCHAR UNIQUE NOT NULL PRIMARY KEY,
departure_time TIME(0) NOT NULL,
departure_airport VARCHAR NOT NULL REFERENCES aeroporto(codice),
arrival_time TIME(0) NOT NULL,
arrival_airport VARCHAR NOT NULL REFERENCES aeroporto(codice),
airline VARCHAR NOT NULL REFERENCES airlines(airline_name)
);
我需要在数据库中显示从所有机场出发的航空公司。有什么建议吗?您可以使用聚合并计算
离港\u机场
:
select v.airline
from volo v
group by v.airline
having count(distinct departure_airport) = (select count(*) from airport);
谢谢,太好了!