How to insert a duplicate value in primary key column? - sql

Question

I have a table that has primary key on first column, but when I see the data available of this table, I find that records are repeated include primary key data. I want to know how can it be possible? Does primary column has repeated data in SQL Server 2008?
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
SET ANSI_PADDING ON
GO
CREATE TABLE [dbo].[DemoTbl](
[ProcedureId] [int] NOT NULL,
[ProcedureName] [nvarchar](100) NOT NULL,
[VersionNo] [char](5) NULL,
[PublishDate] [datetime] NULL,
[PublishUser] [varchar](50) NULL,
[SpecialtyId] [int] NOT NULL,
[ProcedureNumber] [varchar](20) NULL,
[PowerpointName] [nvarchar](100) NULL,
[Duration] [int] NOT NULL,
[LanguageId] [int] NOT NULL,
[TierId] [smallint] NOT NULL,
[PrintPdf] [bit] NULL,
[PresentationModeId] [tinyint] NULL,
CONSTRAINT [pk_DemoTbl] PRIMARY KEY CLUSTERED
(
[ProcedureId] ASC,
[LanguageId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
SET ANSI_PADDING OFF
GO
ALTER TABLE [dbo].[DemoTbl] WITH CHECK ADD FOREIGN KEY([PresentationModeId])
REFERENCES [dbo].[DemoTbl] ([PresentationModeId])
GO
ALTER TABLE [dbo].[DemoTbl] WITH CHECK ADD CONSTRAINT [FK_DemoTbl_Specialty] FOREIGN KEY([SpecialtyId])
REFERENCES [dbo].[Specialty] ([SpecialtyId])
GO
ALTER TABLE [dbo].[DemoTbl] CHECK CONSTRAINT [FK_DemoTbl_Specialty]
GO
ALTER TABLE [dbo].[DemoTbl] WITH CHECK ADD CONSTRAINT [FK_DemoTbl_TierMaster] FOREIGN KEY([TierId])
REFERENCES [dbo].[TierMaster] ([TierId])
GO
ALTER TABLE [dbo].[DemoTbl] CHECK CONSTRAINT [FK_DemoTbl_TierMaster]
GO
ALTER TABLE [dbo].[DemoTbl] ADD CONSTRAINT [DF_DemoTbl_CreationDate] DEFAULT (getdate()) FOR [CreationDate]
GO
ALTER TABLE [dbo].[DemoTbl] ADD CONSTRAINT [DF_DemoTbl_ModifiedDate] DEFAULT (getdate()) FOR [ModifiedDate]
GO
ALTER TABLE [dbo].[DemoTbl] ADD CONSTRAINT [DF_DemoTbl_IsActive] DEFAULT ((1)) FOR [IsActive]
GO
ALTER TABLE [dbo].[DemoTbl] ADD CONSTRAINT [DF_DemoTbl_LanguageId] DEFAULT ((1)) FOR [LanguageId]
GO
ALTER TABLE [dbo].[DemoTbl] ADD CONSTRAINT [DF_DemoTbl_ManageContent] DEFAULT ('false') FOR [ManageContent]
GO
ALTER TABLE [dbo].[DemoTbl] ADD CONSTRAINT [DF__Procedure__Print__1B14C01D] DEFAULT ((1)) FOR [PrintPdf]
GO

Answer 1

No, it is not possible in SQL Server to insert records that have duplicate values in the Primary Key.

Answer 2

It is not possible to have more than one row in the same table with the same primary key (PK).
If you are doing a SELECT and getting more than one row with the same PK could be because:
That table actually does not have a PK, maybe it was not properly created. You can check this by doing the following (it should return the PK column(s)):
SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE table_name = 'TableName' AND COLUMN_KEY='PRI';
The SELECT statement is not correct. Maybe you are selecting from two or more tables and you are not relating them correctly.
To clarify, you can do the following:
1- Create a new table:
CREATE TABLE IF NOT EXISTS `Customer` (
`id` int(4),
`name` varchar(20),
`surname` varchar(40),
`phone` int(9),
PRIMARY KEY (`id`)
) ENGINE=INNODB;
Now you have a new table for storing customers identified by an ID.
2- Let's add some customers:
INSERT INTO Customer VALUES(111, 'John', 'White', 123456789),
(222, 'Bianca', 'Williams', 987654321),
(333, 'Mikel', 'Peterson', 421345642),
(444, 'Jolene', 'Gomez', 948113552);
3- If you try to insert a customer with an existing PK (id) you will get an error:
INSERT INTO Customer VALUES (222, 'Paul', 'Brown', 123412345);
4- In order to check the final table, you can do the following select:
SELECT * FROM Customer;

Answer 3

No it is not possible to have duplicate primary keys if the primary key constraint has been set to True.
Further to prevent duplicate primary keys set the Identity Specification to True

Answer 4

If this table is an intermediate table in a many to many connection the original columns are foreign keys and able to accept many instances of the same prodId(the whole point of the exercise). If someone then slams a PK on that column then no more duplicates can be added but if you query it the table will still return the original stuff in this guys screenshot.
This scenario can be seen in the Northwind sample database between Products and orders (OrderDetails table has composite PK on OrderID, ProdID but still shows duplicates of both). The PK was added afterwards, after data had been added.
The intermediate table is a link between the Many-to-Many tables and in general doesn't need a PK. Normalization 101.

Answer 5

For PK Constraint it create a Unique Index (Clustered / non Clustered ) on defined PK. If we disable indexes before loading that include PK Unique Index as well than we can insert duplicate PK in the column because the PK constraint is disabled. So while disabling Indexes please avoid PK index not be disable "is_primary_key=0 to disable all other indexes"

Answer 6

Tested -> it's possible if we create a primary key with nonclustered index. If we disable this index we will be able to insert duplicated record then. But - it won't be possible to enable (rebuild) the index back with duplicated values on primary key