MySQL 5.7 Release Notes
DECLARE var_name [, var_name] ... type [DEFAULT value]
This statement declares local variables within stored programs.
To provide a default value for a 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 Section 13.1.16, “CREATE PROCEDURE and CREATE FUNCTION Statements”.
Variable declarations must appear before cursor or handler declarations.
Local variable names are not case-sensitive. Permissible characters and quoting rules are the same as for other identifiers, as described in Section 9.2, “Schema Object Names”.
The scope of a local variable is the
BEGIN ...
END block within which 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.
For examples of variable declarations, see Section 13.6.4.2, “Local Variable Scope and Resolution”.