Creating database relationships while designing tables?

Creating database relationships while designing tables?

Hi Nadeemrao,

I'll try to explain it in a simple way: 

• One to one relationship:
• It means each row in Table A is linked to only one row in Table B.
• For example:
• Table A:
• user_id     first_name     last_name
• 1                 brad                pit
• Table B:
• user_id           email_ad                password
• 1                       ****@mailcom.     1234
• The user_id 1 of Table B is brad pit in Table B. This type of relationship is actually not often used in real world. Maybe in MS Access this is useful because of the limited number of columns per table issue. In order to accommodate more than 255 columns we could split the table into two and create a one to one relationship.
• One to Many Relationship:
• It means each row in Table A can have zero, one, or many related rows in Table B but not vice versa. This kind of relationship are also referred as parent and child relationship or master and details relationship. This type of relationship is the most commonly used model.
• For example:
• Orders Table:
• Order_id        Customer_Name           Delivery_Date
• 1                       brad pit                            1/1/2012
• Order_Details Table:
• Order_id       Item_id        Quantity
• 1                     1                    5
• 1                      2                   1
• Many to Many Relationship:
• It means each row in Table A can have many related rows in Table B and vice versa.
• For example:
• Reusing the Orders table, and Order_Details table above, we add Items table.
• Items Table:
• Item_id         Description
• 1                    sunglass
• 2                    t-shirt
• The Order_Details Table above created links to Orders table and Items table and causes the many to many model.  

Hope this helps.