Beyond the basic select statement: Using the WITH clause inline PL/SQL

For years I used the basic select statement:

SELECT A.C1, A.C2, B.C1, B.C2, <…> FROM TAB1 A, TAB2 B WHERE A.C1 = B.C1;

Sometimes this basic select statement would not answer my question. You can make a select statement quite complicated, but then it gets unreadable and difficult to maintain. The WITH clause helps out quite a bit



FUNCTION monthly_amt(pamt number)
RETURN number IS
x number;
     x := pamt*2;
     RETURN x;
SELECT pay22, monthly_amt(pay22)
  FROM policys;

create or replace function
  monthly_amt (pamt number) return number is
  x number;
  x := pamt*2;
  return x;
select pay22, monthly_amt(pay22)
from policys;

We are going to start this discussion with the assumption that Query A and Query B are equivalent with caveats. The rules associated with using an inline function is the inline function will always take precedence over a stored function.

The results of Query A returned pay22 and the result of the inline function monthly_amt.


Query B Returns pay22 and the results of the stored function monthly_amt.


But what if the stored function returns a different value the argument * 2?

First we will redefine the stored function monthly_amt to return argument * 10. When using WITH to include an inline function, the inline function will always take precedence over a stored function with the same name.


Now we will call the stored function monthly_amt and not making any reference to an inline function. As expected the stored function returns argument * 10.


How would we use this? PL/SQL supports overloading functions; however both the stored function and the inline function have the same name and use the same arguments. I see using the inline function when: A) creating a stored function is not an option. I worked in one shop a while back where it was against policy to store PL/SQL in the database. B) when you have to overload a stored function. C) When you need / want to read the PL/SQL being executed.