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sql server alter table command to add primary key

Posted on 2016-08-22
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Last Modified: 2016-08-22
I'm using sql server 2008.

I read this article:
http://stackoverflow.com/questions/2626158/why-use-multiple-columns-as-primary-keys-composite-primary-key

I have this create table script
CREATE TABLE Persons
(
    P_Id int NOT NULL,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255),
    Address varchar(255),
    City varchar(255),
    CONSTRAINT pk_PersonID PRIMARY KEY (P_Id,LastName)
)

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When I run this script that creates a table with two primary key columns that looks like this:

table
I read that on a sql server table on some other article, that you can only have one primary key, but you can have multiple columns in your primary key.

If I want to have the City column also be a primary key column.

Any know the syntax for the Alter Table command so that after I create the table with the script above I can then use the Alter Table command to then add the City column as one of the primary key columns?
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Question by:maqskywalker
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Accepted Solution

by:
Jim Horn earned 500 total points
ID: 41765572
>If I want to have the City column also be a primary key column.
Drop the PK, change City from NULL to NOT NULL, then recreate the PK

ALTER TABLE Persons
DROP CONSTRAINT pk_PersonID
GO

ALTER TABLE Persons
ALTER COLUMN City varchar(255) NOT NULL
GO

ALTER TABLE Persons
ADD CONSTRAINT pk_PersonID PRIMARY KEY (P_Id,LastName, City) 
GO

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by:maqskywalker
ID: 41765587
Thanks.
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