Which type of join compares columns using only the = operator?

An equijoin is a type of join that compares columns from one table to another using only the equality operator (=). This means that it retrieves rows from both tables where the values in the specified columns match exactly. Equijoins are commonly used in SQL and are often employed to combine related data from different tables based on a common column, helping to create meaningful relationships in a relational database.

In contrast, other types of joins serve different purposes. A non-equijoin allows for comparisons that involve operators other than the equality operator, like less than (<), greater than (>), or any other relational operators. Outer joins, which may be inner or left, right, or full outer, include non-matching rows based on the join conditions, which can expand the result set beyond just those with equal column values. An inner join, while it can sometimes be equijoin, is a broader category that includes any type of join that returns records with matching values in both tables but does not strictly limit itself to the equality operator for conditions.

Understanding the distinct characteristics of each join type helps in appropriately applying them in database queries to extract the needed data accurately.