How to append result from select to resultset? - oracle

Question

I have the following tables:
Table 1 - NODES (I access it through a DB_LINK):
SITE_ID LATITUDE LONGITUDE
ABC123 21.018 -89.711
CDE456 20.35 -87.349
FGH789 20.258 -87.406
ABB987 18.54 -88.302
CFF546 18.542 -88.273
GHT553 18.52 -88.311
Table 2 - LINKS
ID SITE_A SITE_B STATUS NAME LINK_TYPE REGION ---> Many other fields
1 ABC123 GHT553
2 FGH789 CFF546
3 CDE456 ABC123
4 CFF546 GHT553
Table 3 - RESULT (This is what I want to achieve) - No matter the order
LINK_ID SITE_A_ID LAT_SITE_A LON_SITE_A SITE_B_ID LAT_SITE_B LON_SITE_B
1 ABC123 21.018 -89.711 GHT553 18.52 -88.311
2 FGH789 20.258 -87.406 CFF546 18.542 -88.273
3 CDE456 20.35 -87.349 ABC123 21.018 -89.711
4 CFF546 18.542 -88.273 GHT553 18.52 -88.311
(Plus several other fields, which means no trouble for me)
This is what I have tried:
SELECT RES2.*, SAM2.LATITUDE LAT_SITE_B, SAM2.LONGITUDE LON_SITE_B FROM(
SELECT RES1.*, NOD.LATITUDE LAT_SITE_A, NOD.LONGITUDE LON_SITE_A FROM(
SELECT ID, SITE_A, SITE_B, STATUS, NAME, LINK_TYPE FROM LINKS
WHERE SITE_A IS NOT NULL AND SITE_B IS NOT NULL AND REGION IN (8,6)
)RES1, NODES#NODES_DBLINK NOD WHERE RES1.SITE_A = NOD.SITE_ID
)RES2, NODES#NODES_DBLINK NOD2
WHERE RES2.SITE_B = NOD2.SITE_ID;
Until the SELECT RES1.\*, everything works fine, but when I add the SELECT RES2.\*, it takes too long without returning anything.

Answer 1

From the textual part of your question, this query will generate the result you want:
SELECT links.id AS link_id,
node_a.site_id AS site_a_id,
node_a.latitude AS lat_site_a,
node_a.longitude AS lon_site_a,
node_b.site_id AS site_b_id,
node_b.latitude AS lat_site_b,
node_b.longitude AS lon_site_b
FROM links
INNER JOIN nodes#nodes_dblink node_a ON (links.site_a = node_a.site_id)
INNER JOIN nodes#nodes_dblink node_b ON (links.site_b = node_b.site_id)
ORDER BY links.id;
From the query you posted it seems you have some other criteria to include too which might mean you want something more like this:
SELECT links.id AS link_id,
node_a.site_id AS site_a_id,
node_a.latitude AS lat_site_a,
node_a.longitude AS lon_site_a,
node_b.site_id AS site_b_id,
node_b.latitude AS lat_site_b,
node_b.longitude AS lon_site_b
FROM links
INNER JOIN nodes#nodes_dblink node_a ON (links.site_a = node_a.site_id)
INNER JOIN nodes#nodes_dblink node_b ON (links.site_b = node_b.site_id)
WHERE links.site_a IS NOT NULL
AND links.site_b IS NOT NULL
AND links.region IN (8, 6)
ORDER BY links.id;
Hope it helps...
EDIT:
If your DB link is an issue, try to return only the data you're going to need over the link in advance either by creating a view on the remote DB or a materialised view on the local DB.
If that isn't practical then check the relative explain plans for the query above against this one and see if it is any better:
WITH node_data
AS (SELECT site_id,
latitude,
longitude
FROM nodes#nodes_dblink node
WHERE EXISTS (SELECT 1
FROM links
WHERE links.site_a = node.site_id
OR links.site_b = node.site_id))
SELECT links.id AS link_id,
node_a.site_id AS site_a_id,
node_a.latitude AS lat_site_a,
node_a.longitude AS lon_site_a,
node_b.site_id AS site_b_id,
node_b.latitude AS lat_site_b,
node_b.longitude AS lon_site_b
FROM links
INNER JOIN node_data node_a ON (links.site_a = node_a.site_id)
INNER JOIN node_data node_b ON (links.site_b = node_b.site_id)
WHERE links.site_a IS NOT NULL
AND links.site_b IS NOT NULL
AND links.region IN (8, 6)
ORDER BY links.id;