问题
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)
回答1:
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'
回答2:
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
回答3:
-- 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.
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
回答4:
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)
回答5:
There is already an primary key in your table. You can't just add primary key,otherwise will cause error. Because there is one primary key for sql table.
First, you have to drop your old primary key.
MySQL:
ALTER TABLE Persion
DROP PRIMARY KEY;
SQL Server / Oracle / MS Access:
ALTER TABLE Persion
DROP CONSTRAINT 'constraint name';
You have to find the constraint name in your table. If you had given constraint name when you created table,you can easily use the constraint name(ex:PK_Persion).
Second,Add primary key.
MySQL / SQL Server / Oracle / MS Access:
ALTER TABLE Persion ADD PRIMARY KEY (PersionId,Pname,PMID);
or the better one below
ALTER TABLE Persion ADD CONSTRAINT PK_Persion PRIMARY KEY (PersionId,Pname,PMID);
This can set constraint name by developer. It's more easily to maintain the table.
I got a little confuse when i have looked all answers. So I research some document to find every detail. Hope this answer can help other SQL beginner.
Reference:https://www.w3schools.com/sql/sql_primarykey.asp
回答6:
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)
回答7:
Necromancing.
Just in case anybody has as good a schema to work with as me...
Here is how to do it correctly:
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
回答8:
Please try this-
ALTER TABLE TABLE_NAME DROP INDEX `PRIMARY`, ADD PRIMARY KEY (COLUMN1, COLUMN2,..);
回答9:
Try using this code:
ALTER TABLE `table name`
CHANGE COLUMN `column name` `column name` datatype NOT NULL,
ADD PRIMARY KEY (`column name`) ;
回答10:
ALTER TABLE TABLE_NAME ADD PRIMARY KEY(`persionId`,`Pname`,`PMID`)
来源：https://stackoverflow.com/questions/11794659/add-primary-key-to-existing-table