Add primary key to existing table

I have an existing table called `Persion`. In this table I have 5 columns:

- persionId
- Pname
- PMid
- Pdescription
- Pamt

When I created this table, I set `PersionId` and `Pname` as the **primary key**.

I now want to include one more column in the primary key - PMID. How can I write an `ALTER` statement to do this? (I already have 1000 records in the table)

drop constraint and recreate it



alter table Persion drop CONSTRAINT <constraint_name>

alter table Persion add primary key (persionId,Pname,PMID)


edit:

you can find the constraint name by using the query below:


select OBJECT_NAME(OBJECT_ID) AS NameofConstraint
FROM sys.objects
where OBJECT_NAME(parent_object_id)='Persion'
and type_desc LIKE '%CONSTRAINT'

I think something like this should work

-- drop current primary key constraint
ALTER TABLE dbo.persion
DROP CONSTRAINT PK_persionId;
GO

-- add new auto incremented field
ALTER TABLE dbo.persion
ADD pmid BIGINT IDENTITY;
GO

-- create new primary key constraint
ALTER TABLE dbo.persion
ADD CONSTRAINT PK_persionId PRIMARY KEY NONCLUSTERED (pmid, persionId);
GO

The PRIMARY KEY constraint uniquely identifies each record in a database table.
Primary keys must contain UNIQUE values and column cannot contain NULL Values.

-- DROP current primary key
ALTER TABLE tblPersons DROP CONSTRAINT <constraint_name>
Example:
ALTER TABLE tblPersons
DROP CONSTRAINT P_Id;


-- ALTER TABLE tblpersion
ALTER TABLE tblpersion add primary key (P_Id,LastName)

-- create new primary key constraint
ALTER TABLE dbo.persion
ADD CONSTRAINT PK_persionId PRIMARY KEY NONCLUSTERED (pmid, persionId);

is a better solution because you have control over the naming of the primary_key.


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It's better than just using

ALTER TABLE Persion ADD PRIMARY KEY(persionId,Pname,PMID)

which yeilds randomized names and can cause problems when scripting out or comparing databases

Necromancing.<br />
Just in case anybody has as good a schema to work with as me...<br />
Here is how to do it correctly:<br />

In this example, the table name is dbo.T_SYS_Language_Forms, and the column name is LANG_UID


-- First, chech if the table exists...
IF 0 < (
SELECT COUNT(*) FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_TYPE = 'BASE TABLE'
AND TABLE_SCHEMA = 'dbo'
AND TABLE_NAME = 'T_SYS_Language_Forms'
)
BEGIN
-- Check for NULL values in the primary-key column
IF 0 = (SELECT COUNT(*) FROM T_SYS_Language_Forms WHERE LANG_UID IS NULL)
BEGIN
ALTER TABLE T_SYS_Language_Forms ALTER COLUMN LANG_UID uniqueidentifier NOT NULL

-- No, don't drop, FK references might already exist...
-- Drop PK if exists (it is very possible it does not have the name you think it has...)
-- ALTER TABLE T_SYS_Language_Forms DROP CONSTRAINT pk_constraint_name
--DECLARE @pkDropCommand nvarchar(1000)
--SET @pkDropCommand = N'ALTER TABLE T_SYS_Language_Forms DROP CONSTRAINT ' + QUOTENAME((SELECT CONSTRAINT_NAME FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS
--WHERE CONSTRAINT_TYPE = 'PRIMARY KEY'
--AND TABLE_SCHEMA = 'dbo'
--AND TABLE_NAME = 'T_SYS_Language_Forms'
----AND CONSTRAINT_NAME = 'PK_T_SYS_Language_Forms'
--))
---- PRINT @pkDropCommand
--EXECUTE(@pkDropCommand)
-- Instead do
-- EXEC sp_rename 'dbo.T_SYS_Language_Forms.PK_T_SYS_Language_Forms1234565', 'PK_T_SYS_Language_Forms';

-- Check if they keys are unique (it is very possible they might not be)
IF 1 >= (SELECT TOP 1 COUNT(*) AS cnt FROM T_SYS_Language_Forms GROUP BY LANG_UID ORDER BY cnt DESC)
BEGIN

-- If no Primary key for this table
IF 0 =
(
SELECT COUNT(*) FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS
WHERE CONSTRAINT_TYPE = 'PRIMARY KEY'
AND TABLE_SCHEMA = 'dbo'
AND TABLE_NAME = 'T_SYS_Language_Forms'
-- AND CONSTRAINT_NAME = 'PK_T_SYS_Language_Forms'
)
ALTER TABLE T_SYS_Language_Forms ADD CONSTRAINT PK_T_SYS_Language_Forms PRIMARY KEY CLUSTERED (LANG_UID ASC)
;

END -- End uniqueness check
ELSE
PRINT 'FSCK, this column has duplicate keys, and can thus not be changed to primary key...'
END -- End NULL check
ELSE
PRINT 'FSCK, need to figure out how to update NULL value(s)...'
END

Try using this code:

ALTER TABLE `table name`
CHANGE COLUMN `column name` `column name` datatype NOT NULL,
ADD PRIMARY KEY (`column name`) ;

ALTER TABLE TABLE_NAME ADD PRIMARY KEY(`persionId`,`Pname`,`PMID`)

If you add primary key constraint

ALTER TABLE <TABLE NAME> ADD CONSTRAINT <CONSTRAINT NAME> PRIMARY KEY <COLUMNNAME>

for example:

ALTER TABLE DEPT ADD CONSTRAINT PK_DEPT PRIMARY KEY (DEPTNO)

Please try this-

ALTER TABLE TABLE_NAME DROP INDEX `PRIMARY`, ADD PRIMARY KEY (COLUMN1, COLUMN2,..);