Declaring local variables

To declare a local variable’s name and datatype use:

declare @variable_name datatype 
   [, @variable_name datatype]...

The variable name must be preceded by the @ sign and conform to the rules for identifiers. Specify either a user-defined datatype or a system-supplied datatype other than text, image, or sysname.

In terms of memory and performance, this is more efficient:

declare @a int, @b char(20), @c float

than this:

declare @a int
declare @b char(20)
declare @c float