性能模式 user_defined_functions 表包含有关当前已安装的可加载函数的信息：The Performance Schema user_defined_functions table contains information about the currently installed loadable functions:

SELECT * FROM performance_schema.user_defined_functions;

mysql.func 系统表也列出了已安装的可加载函数，但仅限于使用 CREATE FUNCTION 安装的函数。user_defined_functions 表列出了使用 CREATE FUNCTION 安装的可加载函数，以及由组件或插件自动安装的可加载函数。这个区别使得 user_defined_functions 比 mysql.func 更适合用于检查已安装的可加载函数。参见 第 29.12.22.10 节，“user_defined_functions 表”。The mysql.func system table also lists installed loadable functions, but only those installed using CREATE FUNCTION. The user_defined_functions table lists loadable functions installed using CREATE FUNCTION as well as loadable functions installed automatically by components or plugins. This difference makes user_defined_functions preferable to mysql.func for checking which loadable functions are installed. See Section 29.12.22.10, “The user_defined_functions Table”.