Shortly column definition

Question

This is a biggest stupid question, but...
I would like to create a funtion that return a "field" for to put a column into a select. I will explian with an example:
my field (that usually write into a select):
NVL(ROUND(SUM(DECODE(field1,0,DECODE(field2,'T',myfield)))),0)
So, my problem is that I have a lot of this field and I would like to create a function for to have a shortly select command
for example, starting from:
SELECT
NVL(ROUND(SUM(DECODE(field1,0,DECODE(field2,'T',myfield1)))),0)
NVL(ROUND(SUM(DECODE(field1,0,DECODE(field2,'T',myfield2)))),0)
NVL(ROUND(SUM(DECODE(field1,0,DECODE(field2,'T',myfield3)))),0)
FROM TABLE1, TABLE2
WHERE
join TABLE1 with TABLE2
I would like to arrive to:
SELECT myfunction(myfield1), myfunction(myfield2), myfunction(myfield3)
I will create a function that return a string for to put it into the select or there is another solution for to have the myfield really that can be correctly calculated into the SELECT command ??
thanks in advance for your help and best regards.
Roberto

Answer 1

You don't make quite clear where these fields come from (tables have columns, forms have fields) but you could do something like this:
SQL> r
  1  CREATE OR REPLACE FUNCTION my_function (p1 IN VARCHAR2, p2 IN VARCHAR2)
  2     RETURN NUMBER
  3  AS
  4     default_value CONSTANT NUMBER := 999;
  5     return_value NUMBER;
  6  BEGIN
  7     IF p1 IS NULL
  8     THEN
  9        return_value := 0;
10     ELSIF p1 = 0
11     THEN
12        IF p2 = 'T'
13        THEN
14           return_value := default_value;
15        ELSE
16           return_value := p2;
17        END IF;
18     ELSE
19        return_value := p1;
20     END IF;
21     RETURN round(return_value);
22* END my_function;
Function created.
SQL> select sum(my_function( col1, col2)) FROM t1
  2  /
SUM(MY_FUNCTION(COL1,COL2))
                         21
SQL> Note that you cannot write aggregating functions, so you have to use SUM in the select statement.
Two additional points:
[list]
[*]If you are using 8i you don't need to declare the RESTRICT_REFERENCES pragma.
[*]If you want to do dataconversion with this thing it might be worth looking at the CREATE OPERTATOR functionality to create an overloaded function.
[list]
Cheers, APC