SQL Server includes a number of "System Functions" as well as more typical functions with the product. Some of these are used often and are fairly clear right from the beginning in terms of how to use them. Others, though, are both rarer in use and more cryptic in nature.
In this appendix, we'll try to clarify the use of most of these functions in a short, concise manner.
Just as an FYI, in prior releases, many system functions were often referred to as "Global Variables." This was a misnomer, and Microsoft has striven to fix it over the last few releases—changing the documentation to refer to them by the more proper "system function" name. Just keep the old terminology in mind in case any old fogies (such as myself) find themselves referring to them as Globals.
The T-SQL functions available in SQL Server 2008 fall into the following categories:
Legacy "system" functions
Date and time functions
Text and image functions
In addition, we have the
OVERoperator, which, while largely working as a ranking tool, can be applied to other forms of T-SQL functions (most notably aggregates). While I only discuss it as part of the ranking functions, you may see it referenced several other places in this appendix.