3.
How many types of relationships can be created in Base? Explain each
of the them.
4.
What do you mean by Sorting? In how many ways it can be done?
Answers
Answer:
We are related to things around us in some or the other way. We are related to our family, friends, etc and these relationships are of different kinds. For example, you and your father are related. There is a parent-child relationship between you. You have only one father but he may have many children. You and your siblings are related. You and your teacher are related. The teacher teaches you as well as many other students. You also study from different teachers.
Database relationships are also very similar to such relationships. We are done with the ER model and we also know about the Entity. Now, in this blog, we will see the database relationships i.e. the second part of the ER model in details.
Relationship in DBMS
Any association between two entity types is called a relationship. Entities take part in the relationship. It is represented by a diamond shape.
For example, A teacher teaches students. Here, "teaches" is a relationship and this is the relationship between a Teacher entity and a Student entity.
We have two entity types of 'Customer'(Customer_id, Name, City, Phone) and 'Account'(Account_no, Type, Balance). We store the data of 'Customer' in one table and his accounts details in the 'Account' table. Now, to link these two tables we need to insert the primary key 'Customer_id' of the 'Customer' table in the 'Account' table. This key acts as a foreign key for the 'Account' table and refers to a column with the same name in the 'Customer' table. This is how a relationship between two tables is established. There are three types of relationships that can exist between two entities.
One-to-One Relationship
One-to-Many or Many-to-One Relationship
Many-to-Many Relationship
One-to-One Relationship
Such a relationship exists when each record of one table is related to only one record of the other table.
For example, If there are two entities ‘Person’ (Id, Name, Age, Address)and ‘Passport’(Passport_id, Passport_no). So, each person can have only one passport and each passport belongs to only one person.
Such a relationship is not very common. However, such a relationship is used for security purposes. In the above example, we can easily store the passport id in the ‘Person’ table only. But, we make another table for the ‘Passport’ because Passport number may be sensitive data and it should be hidden from certain users. So, by making a separate table we provide extra security that only certain database users can see it.
One-to-Many or Many-to-One Relationship
Such a relationship exists when each record of one table can be related to one or more than one record of the other table. This relationship is the most common relationship found. A one-to-many relationship can also be said as a many-to-one relationship depending upon the way we view it.
For example, If there are two entity type ‘Customer’ and ‘Account’ then each ‘Customer’ can have more than one ‘Account’ but each ‘Account’ is held by only one ‘Customer’. In this example, we can say that each Customer is associated with many Account. So, it is a one-to-many relationship. But, if we see it the other way i.e many Account is associated with one Customer then we can say that it is a many-to-one relationship.
3 Answer.. There are three types of relationships between the data you are likely to encounter at this stage in the design: one-to-one, one-to-many, and many-to-many. To be able to identify these relationships, you need to examine the data and have an understanding of what business rules apply to the data and tables.
4. Answer.. Data sorting is any process that involves arranging the data into some meaningful order to make it easier to understand, analyze or visualize. When working with research data, sorting is a common method used for visualizing data in a form that makes it easier to comprehend the story the data is telling.