Change Primary Key to Composite Key (Primary Key already exists)

问题

I am trying to change the primary key of a table in my SQL database from the existing key to a composite key, which does not include the existing column. The following code is not working due to the following error messages:

DROP PRIMARY KEY:

Incorrect Syntax near PRIMARY. Expecting COLUMN, CONSTRAINT, ID, or QUOTED_ID

ADD PRIMARY KEY:

Incorrect Syntax near PRIMARY. Expecting ID

T-SQL code:

ALTER TABLE AgentIdentification 
DROP PRIMARY KEY Number, 
ADD PRIMARY KEY (AgentId, IdIndicator)

EDIT

I was able to accomplish this by using the following two query statements

ALTER TABLE AgentIdentification 
DROP CONSTRAINT [PK_AgentId_Id]
GO

ALTER TABLE AgentIdentification
ADD CONSTRAINT pk_PersonID PRIMARY KEY (AgentId, IdIndicator)

Instead of requesting that SQL "DROP PRIMARY KEY" I needed to tell it to "DROP CONSTRAINT", also separating these two actions into two queries helped.

回答1:

    /* For SQL Server/Oracle/MS ACCESS */
    ALTER TABLE  AgentIdentification 
    DROP CONSTRAINT PK_Table1_Col1


    /* For MySql */
    ALTER TABLE  AgentIdentification 
    DROP PRIMARY KEY

To Add primary key :

MySQL / SQL Server / Oracle / MS Access:

ALTER TABLE Table1
ADD CONSTRAINT pk_PersonID PRIMARY KEY (AgentId, IdIndicator)

来源：https://stackoverflow.com/questions/12167689/change-primary-key-to-composite-key-primary-key-already-exists