The capability of retrieving data from multiple tables using a single SQL statement is one of the most powerful and useful features of any RDBMS.
The more tables involved in the SELECT statement, the more complex the SQL.
JOIN is a query in which data is retrieved from more than one table.
A JOIN matches data from two or more tables, based on the values of one or more columns in each table.
Why do we need JOINS?
In a database where tables are normalized, one table may not give all the information about a
particular entity.
So for comprehensive data analysis, we must assemble data from several tables.
The relational model – having made to partition data and put them in different tables for
reducing data redundancy and improving data independence – relies on the JOIN operation to
enable to perform queries that will combine the related data which resides in more than one
table.
So, JOIN is one of the key operations of the relational model.
The process of forming pairs of rows by matching the contents of related columns is called
joining the tables.
The resulting table which contains the data from the tables participating in the joining operation is called the join between the tables.
In a database where tables are normalized, one table may not give all the information about a
particular entity.
So for comprehensive data analysis, we must assemble data from several tables.
The relational model – having made to partition data and put them in different tables for
reducing data redundancy and improving data independence – relies on the JOIN operation to
enable to perform queries that will combine the related data which resides in more than one
table.
So, JOIN is one of the key operations of the relational model.
The process of forming pairs of rows by matching the contents of related columns is called
joining the tables.
The resulting table which contains the data from the tables participating in the joining operation is called the join between the tables.
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