Thank u Svein Erling Tysvaer for your answer
But I want to clear some points

.if u look for using udf's in firebird u will find that they all say
" All input parameters are passed to a UDF by reference "

. in statement "SELECT GetIntValue(a.ID) FROM MyTable a" I don't
expect the ID column of MyTable to be increased because a.ID "I
Think" is variable holdes the current value of column "ID" of table
MyTable (I don't know the actual mechanism for that)

.and if I want UDF that return more than one value how to do that ???

.my example is simple my problem is much bigger !!!!!!!!!!!!!!!!

My regards for u all
Belal Al-hamed