> I, erroneously, put this in a SP and the Firebird accepted with no
> error message, but the questions is, is it possible to to this? (the
> table's name appears twice), would that generate an exception in
> runtime?
>
> UPDATE SERVICOS SERVICOS SET VALOR_TOTAL = VALOR_TOTAL + :xVALOR_ITEM;

Second "name" is considered an alias and is very legal syntax. For
example you can do following:

UPDATE myLongTable t1
SET
t1.myColumn = :someVar
WHERE
t1.someId = (
SELECT anotherId
FROM anotherTable t2
WHERE t2.otherCol = :anotherVar)

Roman