2017_MariaDB and MySQL Common Table Expressions.pdf下载

In the software world, there are standards and implementations of those standards. Sometimes, the implementations come first, features introduced by eager developers trying to advance the state of the art, and they are formally standardized later. Other times, the standard comes first, developed and agreed upon by vendors, developers, and others, and then implementations of the standard—some faithful, others not so much— make their way into production software later on. Common Table Expressions (CTEs) and Window Functions have been in the ANSI SQL standard for a long time. CTEs were introduced way back in the SQL99 version of the standard, and Window Functions were introduced in the SQL2003 version. Other database systems were quick(er) to implement both of them. Oracle, SQL Server, PostgreSQL, and even SQLite have had implementations of these features for years. MariaDB and MySQL were somewhat late to the game, but they now have standardscompliant implementations of Window Functions and Common Table Expressions. MariaDB added them with their MariaDB 10.2 release, which was declared stable (GA) in May 2017. MySQL is introducing them as part of its upcoming 8.0 release, which as I write this is in its Release Candidate phase. The implementations were developed independently of each other, but they both stick close to the standard, so compatibility between them is good. Generally speaking, a query that works in MariaDB will most likely work in MySQL and vice versa. There are some differences, however, which this book notes when they come up.