In SQL Server, the term "nesting level" refers to the depth of nested actions triggered by triggers. When a trigger on a table causes another trigger to be fired, this creates a nesting of triggers. The function TRIGGER_NESTLEVEL() is used to determine the level of nesting for the trigger currently being executed.
Here's a bit more detail on TRIGGER_NESTLEVEL():
Purpose: TRIGGER_NESTLEVEL() is a function in SQL Server that returns the number of triggers executed in a chain of nested triggers. This helps in managing and controlling recursive or nested triggers execution.
Usage: You can use TRIGGER_NESTLEVEL() to:
Prevent excessive nesting which could lead to stack overflow, performance degradation, or logical errors in the application. Control or limit the recursive behavior of triggers by setting a maximum allowed nesting level.