To understand how Cross Apply and Outer Apply work, and why they are needed, it helps to understand what a table-valued function is.Ī table-valued function is a function that returns a single set of data. A feature called Lateral Joins, which is similar, was introduced in MySQL 8.0.14 and PostgreSQL 9.0. The Cross Apply and Outer Apply features are not available in MySQL or PostgreSQL. Oracle then introduced the Cross Apply feature in 12c which was released in June 2013. SQL Server 2005 was released in November 2005. SQL Server and Oracle both support the Cross Apply and Outer Apply feature. Which Databases Support Cross Apply and Outer Apply? It’s different to a Cross Apply due to the treatment of non-matching rows: a Cross Apply is like an inner join and an Outer Apply is like an outer join. It lets you perform an outer join to a “table-valued function”, which is something that an outer join does not support. Outer Apply is an SQL feature that works in a similar way to a join. The feature also works in Oracle databases. We’ll look at what a “table-valued function” is, and how this is different to a join, later in this guide. It lets you join a table to a “table-valued function”, or to join to a subquery that refers to the outer query for each row, which is not possible with joins. How they differ from Inner and Outer JoinsĬross Apply is an SQL feature that was introduced in SQL Server that works in a similar way to a join.Learn all about Cross Apply and Outer Apply in this guide, including: Have you heard of the SQL Cross Apply feature but have no idea what it does? Or are you familiar with how both Cross Apply and Outer Apply work but don’t know how they can work in the real world?

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