Is it best to create third table with primary key of each table as foreign key ? or add foreign key to first table? For example student table and project table each project has many students.
是否最好创建第三个表，每个表的主键作为外键？或者将外键添加到第一个表？例如，学生表和项目表每个项目都有很多学生。
2 个解决方案
#1
3
If you indeed have a 1-many relationship, then you add a foreign key to the first table. For instance:
如果您确实具有1-many关系，则将外键添加到第一个表。例如：
create table students (
. . .
projectId int not null references project(projectId)
);
The not null makes this 1-many. In most cases, you probably want 0/1-many. If so, then remove the not null constraint.
not null使这个1-many。在大多数情况下，您可能需要0/1-many。如果是，则删除非空约束。
You would only introduce a third table (known as an "association table", "junction table", "cross table" and other names) if students could work on more than one project.
如果学生可以处理多个项目，您只会引入第三个表（称为“关联表”，“联结表”，“交叉表”和其他名称）。
Note that you might want a third table if the student-project relationship can change over time. At any given time, a student works on one project, but over time, if the student can work on more than one.
请注意，如果学生 - 项目关系可能随时间发生变化，您可能需要第三个表。在任何时候，学生都在一个项目上工作，但是如果学生可以在一个以上的项目上工作，那么随着时间的推移。
#2
1
If it is one to many just add new column as foreign key (projectId) in student table
如果是一对多，只需在学生表中添加新列作为外键（projectId）
#1
3
If you indeed have a 1-many relationship, then you add a foreign key to the first table. For instance:
如果您确实具有1-many关系，则将外键添加到第一个表。例如：
create table students (
. . .
projectId int not null references project(projectId)
);
The not null makes this 1-many. In most cases, you probably want 0/1-many. If so, then remove the not null constraint.
not null使这个1-many。在大多数情况下，您可能需要0/1-many。如果是，则删除非空约束。
You would only introduce a third table (known as an "association table", "junction table", "cross table" and other names) if students could work on more than one project.
如果学生可以处理多个项目，您只会引入第三个表（称为“关联表”，“联结表”，“交叉表”和其他名称）。
Note that you might want a third table if the student-project relationship can change over time. At any given time, a student works on one project, but over time, if the student can work on more than one.
请注意，如果学生 - 项目关系可能随时间发生变化，您可能需要第三个表。在任何时候，学生都在一个项目上工作，但是如果学生可以在一个以上的项目上工作，那么随着时间的推移。
#2
1
If it is one to many just add new column as foreign key (projectId) in student table
如果是一对多，只需在学生表中添加新列作为外键（projectId）