Have you ever wondered how to build a string with values for an error message?  One would think that RASIERROR could simply take a string that was concatenated together with variables. 

Something like RAISERROR ('My Error' + @myErrorString, 16,1)

Unfortunately, RAISERROR is not as intuitive as this. 

The syntax for RAISERROR is:

RAISERROR ({msg_id | msg_str}{, severity, state}
    [, argument
        [,...n]] )
    [WITH option[,...n]]

Maybe you have seen the arguments passed into the error message string with percent sign.

RAISERROR ('My Error %s', 16,1, @myErrorString)

The % sign indicates the use of a parameter. 

d or i	Signed integer
o	Unsigned octal
p	Pointer
s	String
u	Unsigned integer
x or X	Unsigned hexadecimal

To pad some space a number must be placed infront of the type.

RAISERROR ('My Error %10s', 16,1, @myErrorString,@myErrorString2)

To justify simply use the + or - sign after the % sign.  To pad with a space, use `` (next to the 1 key)

If you pass more than one argument then you must use the percent signs in order. 

RAISERROR ('My Error %10s is not cool %10s', 16,1, @myErrorString,@myErrorString2)