Postgresql 中文操作指南

44.7. Event Trigger Functions in PL/Tcl #

事件触发器函数可以使用 PL/Tcl 编写。PostgreSQL 要求将被用作事件触发器的函数声明为无参数且返回类型 event_trigger 的函数。

Event trigger functions can be written in PL/Tcl. PostgreSQL requires that a function that is to be called as an event trigger must be declared as a function with no arguments and a return type of event_trigger.

触发器管理器的信息通过以下变量传递到函数主体：

The information from the trigger manager is passed to the function body in the following variables:

  • $TG_event

    • The name of the event the trigger is fired for.

  • $TG_tag

    • The command tag for which the trigger is fired.

将忽略触发器函数的返回值。

The return value of the trigger function is ignored.

以下是一个简单的示例事件触发器函数，它将在每次执行支持的命令时引发 NOTICE 消息：

Here’s a little example event trigger function that simply raises a NOTICE message each time a supported command is executed:

CREATE OR REPLACE FUNCTION tclsnitch() RETURNS event_trigger AS $$
  elog NOTICE "tclsnitch: $TG_event $TG_tag"
$$ LANGUAGE pltcl;

CREATE EVENT TRIGGER tcl_a_snitch ON ddl_command_start EXECUTE FUNCTION tclsnitch();