How do I concatenate characters or strings using SQL?

Concatenation (joining 2 or more characters or strings of the same data type) is accomplished using the "+" operator. For example, let's say that I want to join the strings "Able" and "Baker". To do so, I would simply write:

select 'Windows' + 'Vista' as OSName
Running this query would return:

OSName
------------
WindowsVista
OK so far, but what if you want a space between "Windows" and "Vista"? That could be accomplished in 2 ways: Either by including it in one of our existing strings (i.e. "Windows " or " Vista"), as in:

select 'Windows ' + 'Vista' as OSName
or by adding an additional concatenation operator:

select 'Windows' + ' ' + 'Vista' as OSName
Both methods return the desire result:

OSName
-------------
Windows Vista
A more useful example that also demonstrates the "of the same data type" caveat mentioned above:

select 'Today is: ' + convert(varchar(10), getdate(), 101) as Today
would return:

Today
--------------------
Today is: 01/05/2008
However, if we failed to convert result of getdate() into a varchar, we would receive an error similar to:

Today
----------------------
Msg 241, Level 16, State 1, Line 1
Conversion failed when converting datetime from character string.
For additional information, please visit: http://msdn2.microsoft.com/en-us/library/ms177561.aspx