How do I create a table with a two primary keys of

问题:

create table Machine
(
 Machine_ID int primary key,
 Machine_Name varchar(30)
 Machine_Title varchar(30)
)
create table Part
(
 Part_ID int primary key,
 Part_Name varchar(30),
 Part_Description varchar(30)
)

//How do I make this table below?
create table Machine-Part
(
  Machine_ID int foreign key references (Machine.Machine_ID),
  Part_ID int foreign key references (Part.Part_ID)
  Factory_Note varchar(30);
) 

Mysql complains there is a problem with syntax?

Desired Result: have Table 'Machine-Part' use 'Machine_ID' & 'Part_ID' as both primary keys (which are both foreign keys).

回答1:

If you declare the constraint separately (table level), it makes more sense

create table Machine-Part
(
  Machine_ID int NOT NULL ,
  Part_ID int NOT NULL ,
  Factory_Note varchar(30) NULL,

  PRIMARY KEY (Machine_ID, Part_ID),
  UNIQUE INDEX (Part_ID, Machine_ID),
  foreign key (Machine_ID) references (Machine.Machine_ID),
  foreign key (Part_ID) references (Part.Part_ID)
) 

Link tables almost always need a reverse index too

回答2:

Something like this -

CREATE TABLE Machine(
  Machine_ID INT PRIMARY KEY,
  Machine_Name VARCHAR(30),
  Machine_Title VARCHAR(30)
)
ENGINE = INNODB;

CREATE TABLE Part(
  Part_ID INT PRIMARY KEY,
  Part_Name VARCHAR(30),
  Part_Description VARCHAR(30)
)
ENGINE = INNODB;

create table `Machine-Part`(
  Machine_ID int,
  Part_ID int,
  Factory_Note varchar(30),
  CONSTRAINT fk_Machine_ID FOREIGN KEY (Machine_ID) REFERENCES Machine(Machine_ID),
  CONSTRAINT fk_Part_ID FOREIGN KEY (Part_ID) REFERENCES Part(Part_ID)
)
ENGINE = INNODB;

You can find all information on these pages:

• FOREIGN KEY Constraints
• CREATE TABLE Syntax