Question

Need to create a table to hold photos from a current table that I already have but I do not know how to create a foreign key in SQL

Asked by: Mezillinu

I have a table that currently supports 1 photo per product inserted.  I have created this script and will attach it below.  What I do not know how to do because I have never needed to do it is how to build a foreign key to another table which I need to create which will support multiple photos per item.

What I had in mind is to create a table, named tbl_pics which has a foreign unique key to ID.  Could somebody show me how to do it? It is a simple procedure but I have never done it before.

Thanks for your help, all help is appreciated!

GO
/****** Object:  Table [dbo].[tbl_products]    Script Date: 03/07/2008 23:31:09 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[tbl_products](
	[ID] [int] IDENTITY(1,1) NOT NULL,
	[ImgType] [nvarchar](15) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
	[ProductName] [nvarchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
	[ProductDescription] [nvarchar](500) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
	[productPrice] [money] NULL,
	[ImageData] [image] NOT NULL,
 CONSTRAINT [PK_tbl_transaction_images] PRIMARY KEY CLUSTERED 
(
	[ID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

                                  
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Asked On
2008-03-07 at 14:36:23ID23224313
Tags

SQL & ASP.NET

Topics

MS SQL Server

,

SQL Query Syntax

,

.NET

Participating Experts
2
Points
500
Comments
10

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Answers

 

by: chapmandewPosted on 2008-03-07 at 14:50:49ID: 21074791

Sure...here is how you do it....I took you image column out of your first column and added it to the 2nd...you can keep it in the first table if you want...it won't hurt anything.....

The REFERENCES part of the 2nd table (new table) creates your foreign key constraint.

HTH,
Tim

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[tbl_products](
	[ID] [int] IDENTITY(1,1) NOT NULL,
	[ImgType] [nvarchar](15) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
	[ProductName] [nvarchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
	[ProductDescription] [nvarchar](500) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
	[productPrice] [money] NULL,
 
 CONSTRAINT [PK_tbl_transaction_images] PRIMARY KEY CLUSTERED 
(
	[ID] ASC
)
)
GO
CREATE TABLE tbl_ProductImages
(
ImageID INT NOT NULL Primary Key Clustered,
ID INT NOT NULL REFERENCES tbl_products(ID),
[ImageData] [image] NOT NULL
)

                                              
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by: BriCrowePosted on 2008-03-07 at 14:51:56ID: 21074799

I would recommend creating tbl_pics with an IDENTITY column as well.  The query below should populate tbl_pics for you.

INSERT INTO tbl_pics (ProductID, ImageData)
SELECT ID, ImageData FROM tbl_Products

 

by: MezillinuPosted on 2008-03-07 at 14:55:44ID: 21074832

Could you please explain to me why are you taking this approach? I am used to using access - so Since I am new to SQL these things dont actually occour to me :S

 

by: chapmandewPosted on 2008-03-07 at 14:55:48ID: 21074834

good call...forgot to add that


CREATE TABLE tbl_ProductImages
(
ImageID INT IDENTITY(1,1) NOT NULL Primary Key Clustered,
ID INT NOT NULL REFERENCES tbl_products(ID),
[ImageData] [image] NOT NULL

 

by: chapmandewPosted on 2008-03-07 at 14:57:58ID: 21074853

It is standard database design....You use the 2nd table to store the pictures....it is a LOT easier to enter a record into a table rather than to add a field to a table each time a pic is added.  It saves space, and time.  

Here is a link on normalization (why its done).
http://en.wikipedia.org/wiki/Database_normalization

 

by: MezillinuPosted on 2008-03-07 at 14:58:44ID: 21074857

Ahhhhhh, you did not understand me I think!

I wanted another table to be created, with a first picture in tbl_products, and then the other pictures are in another table.

This is because what I had in mind, in my datagrid in ASP.NET, i make a navidational url, "View more pictures of this product" and then when i click that, i open a new window and do "select * from tbl_pics where picID=" & ID of selected row.

Does this make sense? Or do you think that I should put all images in one table?

 

by: chapmandewPosted on 2008-03-07 at 14:59:53ID: 21074867

I would put them in one table...but as I stated earlier, you can keep your image field in  your first table, and just add additional pictures to the new table.....

 

by: MezillinuPosted on 2008-03-07 at 15:04:30ID: 21074902

Ok! I will try this out! It is more than enough help, I am really greatful for all of your help!

Thanks alot have a nice day :-)

 

by: BriCrowePosted on 2008-03-07 at 15:05:21ID: 21074906

Which approach are you refering to?

If you are refering to the addition of an IDENTITY column.  Best practices dictate that you should always have a primary key.  Other than the occasional lookup table I use an IDENTITY (or GUID if using replication) in every table.  I have found through previous experience that the key value should be insignificant to the actual data.  For example if you were creating a table of people it would be reasonable to use something like an SSN as the key but if for some reason you ever had to change the SSN you would have to cascade that value through all referencing tables .  There are several other reasons that I won't go into such as join efficiency and the fact that it makes some queries much easier to write (remove duplicates) etal.

 

by: BriCrowePosted on 2008-03-07 at 15:29:57ID: 21075030

A hybrid of this if you want a primary photo but allow for multiples is to add a reference in the products table to the picture table.  This would allow you the many-to-one relationship but still allow you to designate a primary image for display purposes.  I've done this before with the primary address for a contact.

ALTER TABLE [dbo].[tbl_products]
ADD COLUMN PrimaryPic int NULL tbl_Pics(PicID)

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