How to add composite primary key to table

Question

create table d(id numeric(1), code varchar(2))

创建上表后，如何在两个字段和外键上添加复合主键？

Answer 1

alter table d add constraint pkc_Name primary key (id, code)

should do it. There's lots of options to a basic primary key/index depending on what DB your working with.

Answer 2

In Oracle, you could do this:

create table D (
  ID numeric(1),
  CODE varchar(2),
  constraint PK_D primary key (ID, CODE)
);

Answer 3

The ALTER TABLE statement presented by Chris should work, but first you need to declare the columns NOT NULL . All parts of a primary key need to be NOT NULL .

Answer 4

You don't need to create the table first and then add the keys in subsequent steps. You can add both primary key and foreign key while creating the table:

This example assumes the existence of a table ( Codes ) that we would want to reference with our foreign key.

CREATE TABLE d (
id [numeric](1),
code [varchar](2),
PRIMARY KEY (id, code),
CONSTRAINT fk_d_codes FOREIGN KEY (code) REFERENCES Codes (code)
)

If you don't have a table that we can reference, add one like this so that the example will work:

CREATE TABLE Codes (
    Code [varchar](2) PRIMARY KEY   
    )

NOTE: you must have a table to reference before creating the foreign key.

Answer 5

If using Sql Server Management Studio Designer just select both rows (Shift+Click) and Set Primary Key.