Page 181 - Data Science class 10
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There are many places where these data merging procedures will help you. For example, if you have two different
systems that work in parallel with each other. Suppose you have to do some analysis of the relationship where you
have a legacy system with very poorly formatted data that you are willing to integrate with your new system. This
is where data merging comes into the picture. Let us now learn more about data merging techniques.
4.2. DATA JOINS
We can merge data by applying data joins on the databases in frame. There are three types of data joins which are
as follows:
• One to one Join
• One to many Join
• Many to many Join
• One to One Join: It is used to create a join between two tables in which a single row of the first table can only
be linked to one and only one row of the second table. In the same way, the row of the second table can also be
linked to any row of the first table. In this join, both tables must have primary key columns. It occurs when there
is exactly one record in Table A that corresponds to exactly one record in Table B.
Customer (Table A) Order (Table B)
Rohan Ord 101
Viraj Ord 102
Ananya Ord 103
Divya Ord 105
Suraj Ord 107
Vishal Ord 108
Anaya Ord 109
Aarush Ord 110
• One to Many Join: It is used to create a join between two tables. Any single row of the first table can be linked
to one or more rows of the second table, but the rows of the second table can only link to the only row in the
first table. It is also known as a many to one join.
In this join, one of the tables must have a primary key column that will be associated with all the columns of related
tables. It occurs when each record in Table A can have many linked records in Table B but each record in Table B
may have only one corresponding record in Table A.
Representation of One to Many relational databases:
Person (Table A) Games (Table B)
Rohan Cricket
Viraj Football
Ananya Tennis
Divya Volleyball
Suraj Carrom
Vishal Bowling
Anaya Boxing
Aarush Basketball
• Many to Many Join: It is many to many joins that create a link between two tables. Each row of the first table
can link to any row (or no row) in the second table. In the same way, each row of the second table can also link
to more than one row of the first table. It is also represented as an N:N relationship.
Data Merging 179

