Join in a relational database management program is a data retrieval operation in which a new data table is built from data in two or more existing data tables. The join operation for relational databases is otherwise known as a natural join, and this type of join is characterized by two relations that are connected with their common attributes.
In SQL, an INNER JOIN prevents a Cartesian product from occurring when there are two tables in a query. For each table added to a SQL Query, one additional INNER JOIN is added to prevent a Cartesian product. Thus, for N tables in an SQL query, there must be N−1 INNER JOINS to avoid a Cartesian product.
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Technipages Explains Join
Join in relation to a relational algebra that looks to combine columns from multiple tables in a relational database. It creates a set that can be saved as a table or used as it is. A join serves the purpose of combining columns from one or more tables by adopting values similar to each. ANSI-standard SQL specifies five types of join namely:
- Left outer
- Right outer
- Full outer
- Cross
Join works off the back of the relational database management program that uses operates using a process data with an easy-to-understand concept of a table. A relational database is a type of database that functions using a structure that allows users to identify and access data about another piece of data in the database. Data in a relational database is organized into tables.
The relational model was first designed and proposed by Edgar Codd to serve as an alternative for a general model of data, and subsequently promoted by Chris Date and Hugh Darwen among others and was released in 1995.
Common Uses of Join
- Join has proven to be a very instrumental technique when you want to combine tables.
- Join is a method of relating databases, and it has proven to be very effective over the years.
- It would be impossible to separate Join from relational database management.
Common Misuses of Join
- Join is the only relational model method we have had since the ’90s.