Joins in SQL1 min read


JOINS
 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.


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