SQL：两个表的不同行之间的关系

I'm creating er-diagram for "Airport" database. And I got stick with tables "Flight" and "Airport" . In table "Flight" I have 2 columns: "Departure_place" and "Arrival_ place". Both of it should be connected to values in table "Airport". So, How can I make that in the proper way on er-diagram and on sql?

我正在为“机场”数据库创建er-diagram。我坚持使用桌子“飞行”和“机场”。在表格“飞行”中，我有两列：“Departure_place”和“Arrival_ place”。它们都应该连接到表“Airport”中的值。那么，我怎样才能在er-diagram和sql上以正确的方式实现呢？

1 个解决方案

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I think you are looking for foreign keys. Here is a tutorial for that:

我想你正在寻找外键。这是一个教程：

https://www.w3schools.com/sql/sql_foreignkey.asp

In your case first create the tables:

在您的情况下，首先创建表：

create table flight(
  idFlight int primary key,
  idDeparturePlace int,
  idArrivalPlace int);

create table airport(
  idAirport int primary key);

Now you have to add tow foreign keys. One for idDepaturePlace and one for idArrivalPlace.

现在你必须添加两个外键。一个用于idDepaturePlace，另一个用于idArrivalPlace。

Follow this syntax:

请遵循以下语法：

ALTER TABLE <child table> ADD FOREIGN KEY (<col in child table>) REFERENCES <master table>(<col in master table>);

In your case you have to add this both keys to your flight table:

在您的情况下，您必须将这两个键添加到您的航班表：

ALTER TABLE flight ADD FOREIGN KEY (idDepaturePlace) REFERENCES airport(idAirport);

ALTER TABLE flight ADD FOREIGN KEY (idArrivalPlace) REFERENCES airport(idAirport);

#1

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