Equijoin

Equijoin is a type of database join operation that combines rows from two or more tables based on a matching condition between specified columns. The condition in an equijoin is always an equality comparison, meaning that a row from one table is included in the result set only if the value in the specified join column(s) is exactly equal to the value in the corresponding join column(s) of a row in the other table.

This is the most common type of join and is often the default behavior when a join is specified without an explicit comparison operator. For example, if you have a table of customers and a table of orders, and you want to find all orders placed by a specific customer, you would use an equijoin on the customer ID column present in both tables. The query would look for rows where the customer ID in the customers table matches the customer ID in the orders table.

Equijoins are fundamental to relational database operations as they allow for the retrieval of related data that is spread across multiple tables. They are crucial for building complex queries and ensuring data integrity by linking records through common identifiers. The efficiency of an equijoin often depends on proper indexing of the join columns. If the join columns are indexed, the database can quickly locate matching rows, leading to faster query execution. Without indexes, the database might have to perform a full table scan, which can be significantly slower for large datasets.