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

This statement is used to declare local variables. 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 routine parameters with respect to
data type and overflow checking. See [create-procedure].

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.
