Final answer:
An ANSI join is a type of SQL join that adheres to the ANSI SQL standards, explicitly stating the join type and conditions.
Step-by-step explanation:
An ANSI join refers to the syntax for a join clause in a SQL query that conforms to the American National Standards Institute (ANSI) SQL standard.
This standard outlines how to write SQL code in a way that is consistent across different database systems. ANSI joins explicitly specify the type of join being performed (like INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL JOIN) and the joining condition.
The use of ANSI joins improves the readability and maintainability of SQL code, by clearly outlining the relationships between the tables. Whether there is a performance advantage to using ANSI joins over non-ANSI joins (such as the older, comma-separated syntax) often depends on the database system and its query optimizer.
Most modern database systems will treat ANSI joins and non-ANSI joins the same in terms of execution plans and performance. However, the ANSI syntax is generally preferred for its clarity and cross-database compatibility.
It is often preferred for its readability and maintainability, with no inherent performance advantage over non-ANSI joins, as this depends on the database system's query optimizer.