Substitution for portion of SQL string

Question

This is from a media library that's actually a sandbox for some items I'm using in a real world application. I have a query going into an interactive report with a bit of ugliness in one column like so:
select MEDIATYPE,
m.ID,
NVL2(m.COVER_THUMBNAIL_WIDTH,'<a href = "javascript:popUp2(''f?p=&APP_ID.:12:&SESSION.::&DEBUG.:12:P12_ID:' ||
m.ID || ''',' || NVL2(m.COVER_WIDTH,m.COVER_WIDTH+70,500) || ',' || NVL2(m.COVER_HEIGHT,m.COVER_HEIGHT+100,600) || ');">' ||
'<img src="#OWNER#.DISPLAY_THUMBNAIL?p_id=' || m.ID || '" WIDTH="' ||
NVL2(m.COVER_THUMBNAIL_WIDTH,m.COVER_THUMBNAIL_WIDTH,50) || '" HEIGHT="' ||
NVL2(m.COVER_THUMBNAIL_HEIGHT,m.COVER_THUMBNAIL_HEIGHT,50) || '" ALT="' ||
utl_url.escape(m.TITLE) || '" /></a>','Not Available') CoverImage,
m.TITLE,
m.YEAR,
STUDIO,
SEQUELS.TITLE AS SEQUEL,
PREQUELS.TITLE AS PREQUEL
from
  ALLMEDIA m, ALLMEDIA SEQUELS, ALLMEDIA PREQUELS, STUDIO_LOOKUP, MEDIATYPE_LOOKUP
where
  (STUDIO_LOOKUP.STUDIO_ID = m.STUDIO_ID) AND
  (MEDIATYPE_LOOKUP.MEDIATYPE_ID = m.MEDIATYPE_ID) AND
  (m.SEQUELID = SEQUELS.ID(+)) AND
  (m.PREQUELID = PREQUELS.ID(+));The nastiness is the CoverImage column. This link is something I'm going to need to use in multiple places throughout my application. I isolated it to an individual query, but if I make it an SQL function the state variables don't get evaluated and I end up with &SESSION etc. coming out unprocessed. I've also tried assigning just the code for that column to an application level variable, but the results there aren't as expected.
What is a good approach for taking the code for this one column and making it into something I can use throughout my application? I don't mind having an individual query if that's what is necessary.
Chris

Answer 1

Try using v('') syntax in your function. So, v('APP_SESSION'). If for some reason that does not work, you could always take in an argument or 2 for your function.
Keep in mind that calling a function in a SQL statement will cause the SQL Parser to context-switch between PL/SQL and SQL for every row. This is fine for queries of say 10-50 rows, but if you plan on returning hundreds or thousands of rows on a regular basis, this will be very slow.
If the only thing that will change from row to row is m.id, you could add in a place-holder string in your function like ~ID~, then get creative and do something like this:
with jsCall as (select your_function from dual)
select replace(j.your_function,'~ID~',m.id) coverImage...
  from  ALLMEDIA m, jsCall j, ....This will only run the function once at the beginning of the query. Then you're just doing a SQL replace on the string that is your function for each row.