Syntax:
DECLARE var_name [, var_name] ... type [DEFAULT value]

This statement is used to declare local variables within stored
programs. To provide a default value for the variable, include a
DEFAULT clause. The value can be specified as an expression; it need
not be a constant. If the DEFAULT clause is missing, the initial value
is NULL.

Local variables are treated like stored routine parameters with respect
to data type and overflow checking. See [HELP CREATE PROCEDURE].

Local variable names are not case sensitive.

The scope of a local variable is within the BEGIN ... END block where
it is declared. The variable can be referred to in blocks nested within
the declaring block, except those blocks that declare a variable with
the same name.

URL: http://dev.mysql.com/doc/refman/5.1/en/declare-local-variable.html

