Lesson 11	Built-in functions
Objective	Monitor SQL Server with built-in functions.

Monitor SQL-Server built-in Functions

SQL Server has scalar functions^[1] that can be used to monitor SQL Server. While there are many different functions, the ones we are concerned with are the functions that are useful in monitoring SQL Server's behavior. The following list contains the commonly used functions and a description of what they do.

`@@CONNECTIONS`	returns the number of attempted connections since SQL Server was last booted
`@@CPU_BUSY`	The number of milliseconds that SQL Server was using the CPU since SQL Server started
`@@IDLE`	The number of milliseconds that SQL Server was not working since SQL Server started
`@@IO_BUSY`	The number of milliseconds that SQL Server was processingI/Osince SQL server started
`@@MAX_CONNECTIONS`	The maximum number of simultaneous connections since SQL Server last started
`@@PACKET_ERRORS`	The total number of network packet errors SQL Server had since it last started
`@@PACK_RECEIVED`	The total number of network packets SQL Server received since it last started
`@@PACK_SENT`	The total number of network packets SQL Server sent since it last started
`@@SERVERNAME`	The name of the Microsoft SQL server
`@@SERVICENAME`	The registry key that was used when starting SQL Server
`@@TIMETICKS`	The number of milliseconds per clock tick
`@@TOTAL_ERRORS`	The total number of disk I/O errors SQL Server had since it last started
`@@TOTAL_READ`	The number of disk reads that SQL Server performed since it last started
`@@TOTAL_WRITE`	The number of disk writes that SQL Server performed since it last started.
`@@VERSION`	The version of SQL Server

Function replaces SQL Expression

All of these functions can be used in place of an expression in any SQL statement. When used, these functions return one value, and nothing you do directly affects the value returned. The simplest way to use them is in a select statement, as in the following example:
select @@total_write

For those of you who have used previous versions of SQL Server, these scalar functions that start with an @@ used to be called global variables. You will still see some documentation that refers to them that way.

The following section contains a summary of SQL Functions.

Summary SQL @@functions

How many attempted logins have there been since SQL Server was last booted?	@@CONNECTIONS
How long has SQL Server been using the CPU since startup?	@CPU_BUSY
Has there been any period of time that SQL Server has not been working since startup?	@@IDLE
What is the highest number of simultaneous connections since SQL Server last started?	@@MAX_CONNECTIONS
How many network packet errors have there been?	@@PACKET_ERRORS
How many network packets have been received since it last started?	@@PACK_RECEIVED
How many network packets have been sent?	@@PACK_SENT
What is the SQL Server’s name?	@@SERVERNAME
What registry key was used when starting SQL Server?	@@SERVICENAME
How many network packets have been sent?	@@PACK_SENT
How many milliseconds per clock tick?	@@TIMETICKS
How many disk I/O errors have there been since SQL Server started?	@@TOTAL_ERRORS

The next lesson reviews what you learned in this module.

[1]Scalar functions: A function that returns a single value.