How to reuse a large query without repeating it?

Question

If I have two queries, which I will call horrible_query_1 and ugly_query_2, and I want to perform the following two minus operations on them:

Answer 1

Since you're using Oracle, I'd create Pipelined TABLE functions. The function takes parameters and returns an object (which you have to create) and then you SELECT * or even specific columns from it using the TABLE() function and can use it with a WHERE clause or with JOINs. If you want a unit of reuse (a function) you're not restricted to just returning values (i.e a scalar function) you can write a function that returns rows or recordsets. something like this:

FUNCTION RETURN_MY_ROWS(Param1 IN type...ParamX IN Type)
            RETURN PARENT_OBJECT PIPELINED
            IS
            local_curs cursor_alias; --you need a cursor alias if this function is in a Package
            out_rec ROW_RECORD_OF_CUSTOM_OBJECT:=ROW_RECORD_OF_CUSTOM_OBJECT(NULL, NULL,NULL) --one NULL for each field in the record sub-object
        BEGIN
         OPEN local_curs FOR
          --the SELECT query that you're trying to encapsulate goes here
          -- and it can be very detailed/complex and even have WITH () etc..
        SELECT * FROM baseTable WHERE col1 = x;

   -- now that you have captured the SELECT into a Cursor
   -- here you put a LOOP to take what's in the cursor and put it in the 
   -- child object (that holds the individual records)
          LOOP
         FETCH local_curs --opening the ref-cursor
          INTO out_rec.COL1, 
               out_rec.COL2,
               out_rec.COL3;
        EXIT WHEN local_curs%NOTFOUND;
         PIPE ROW(out_rec); --piping out the Object
        END LOOP;
        CLOSE local_curs;  -- always do this
        RETURN;  -- we're now done
  END RETURN_MY_ROWS;

after you've done that, you can use it like so

SELECT * FROM TABLE(RETURN_MY_ROWS(val1, val2)); 

you can INSERT SELECT or even CREATE TABLE out of it , you can have it in joins.

two more things to mention:

--ROW_RECORD_OF_CUSTOM_OBJECT is something along these lines
CREATE or REPLACE TYPE ROW_RECORD_OF_CUSTOM_OBJECT AS OBJECT
(
     col1 type;
     col2 type;
      ...
     colx type;
 );

and PARENT_OBJECT is a table of the other object (with the field definitions) we just made

create or replace TYPE PARENT_OBJECT IS TABLE OF ROW_RECORD_OF_CUSTOM_OBJECT;

so this function needs two OBJECTs to support it, but one is a record, the other is a table of that record (you have to create the record first).

In a nutshell, the function is easy to write, you need a child object (with fields), and a parent object that will house that child object that is of type TABLE of the child object, and you open the original base-table fetching SQL into a SYS_REFCURSOR (which you may need to alias) if you're in a package and you read from that cursor from a loop into the individual records. The function returns a type of PARENT_OBJECT but inside it packs the records sub-object with values from the cursor.

I hope this works for you (there may be permissioning issues with your DBA if you want to create OBJECTs and Table functions)*/