Change Primary Key

问题

I have a table in Oracle which has following Schema:

City_ID  Name  State  Country  BuildTime  Time

When i declared the table my primary key was both City_ID and the BuildTime but now I want to change the primary key to three columns:

City_ID  BuildTime  Time

How can I change the primary key?

回答1:

Assuming that your table name is city and your existing Primary Key is pk_city, you should be able to do the following:

ALTER TABLE city
DROP CONSTRAINT pk_city;

ALTER TABLE city
ADD CONSTRAINT pk_city PRIMARY KEY (city_id, buildtime, time);

Make sure that there are no records where time is NULL, otherwise you won't be able to re-create the constraint.

回答2:

You will need to drop and re-create the primary key like this:

alter table my_table drop constraint my_pk;
alter table my_table add constraint my_pk primary key (city_id, buildtime, time);

However, if there are other tables with foreign keys that reference this primary key, then you will need to drop those first, do the above, and then re-create the foreign keys with the new column list.

An alternative syntax to drop the existing primary key (e.g. if you don't know the constraint name):

alter table my_table drop primary key;

来源：https://stackoverflow.com/questions/2310561/change-primary-key