Question

I would like to extract a function from a piece of SQL-code which is used multiple times in one query. I’m looking for a functionality which is similar to the following (invented by me) syntax:

with f(x) as (return x+1)
select f(thing1), f(thing2), f(thing3) from things

thing1, thing2, thing3 are integer columns in the table “things” in the example. Also, imagine that f is more complicated than an add-one function.

How do I define a function inside a query?

Answer 1

Declaration of a function in the WITH clause of a query is not possible but according to the information presented at OOW it will be in 12c version. So for now you need to create a function as a schema object whether it would be a stand-alone function or part of a package. For example:

create or replace function F(p_p in number)
return number
is
begin
  return p_p + 1;
end;

And then call it in a query, ensuring that the data type of a column you are passing in to the function as a parameter is of the same data type as the parameter of the function:

select f(col1)
     , f(col2)
     , ...
     , f(coln)
  from your_table