Problems with UNION

Question

Hi,
I'm trying to execute this query:
SELECT silt.ISIN, 
       silt.DESCRIPTION,
       sidm1.BUSINESS_DATE, sidm1.AZIONE, sidm1.CAMBIO, sidm1.EMITTENTE, sidm1.OPZIONE, sidm1.PAESE, sidm1.TASSO, sidt1.VAR_TRIMESTRALE, '|' as "END"
  FROM SPR_ISIN_LIST_TLX silt, spr_isin_drm_mi sidm1, spr_isin_drm_to sidt1
  where "TYPE"='Bon' or "TYPE"='Equ' and silt.ISIN=sidm1.ISIN and silt.ISIN=sidt1.COD_ISIN
UNION
  SELECT silm.ISIN,
       silm.DESCRIPTION,
       sidm2.BUSINESS_DATE, sidm2.AZIONE, sidm2.CAMBIO, sidm2.EMITTENTE, sidm2.OPZIONE, sidm2.PAESE, sidm2.TASSO, sidt2.VAR_TRIMESTRALE, '|' as "END"
  FROM SPR_ISIN_LIST_MOT silm, spr_isin_drm_mi sidm2, spr_isin_drm_to sidt2
  where sidm2.ISIN=silm.isin and sidt2.COD_ISIN=silm.isin
UNION
  SELECT silm1.ISIN, 
       DESCRIPTION,
       sidm3.BUSINESS_DATE, sidm3.AZIONE, sidm3.CAMBIO, sidm3.EMITTENTE, sidm3.OPZIONE, sidm3.PAESE, sidm3.TASSO, sidt3.VAR_TRIMESTRALE, '|' as "END"
  FROM SPR_ISIN_LIST_MTA silm1, spr_isin_drm_mi sidm3, spr_isin_drm_to sidt3
  where "TYPE"='azi' or "TYPE"='quo' and silm1.ISIN=sidm3.ISIN and silm1.ISIN=sidt3.COD_ISIN
UNION
SELECT sila.ISIN,
       SUBSTR(sila.AZIONE, 1, 20) AS DESCRIPTION,
       sidm4.BUSINESS_DATE, sidm4.AZIONE, sidm4.CAMBIO, sidm4.EMITTENTE, sidm4.OPZIONE, sidm4.PAESE, sidm4.TASSO, sidt4.VAR_TRIMESTRALE, '|' as "END"
  FROM SPR_ISIN_LIST_AZIONIESTERE sila, spr_isin_drm_mi sidm4, spr_isin_drm_to sidt4
  where sila.ISIN=sidm4.ISIN and sila.ISIN=sidt4.COD_ISINThe db processes the query for infinitely time without gives me a result.
If I try to execute, singularly, one of the queries that compose what I have wirtten, this single query gives me result, correctly.
Why this problem?
How can execute what I have written correctly?
Thanks a lot.
Bye bye.

Answer 1

Two points:
1. I doubt that you've fetched each of your queries to the end of the result set. They probably return the first rows of the result set in a reasonable amount of time. Depending on the tool you're using you would need to fetch to the end.
2. As already mentioned there is a serious doubt regarding your join criteria. You mix OR and ANDs of the join condition. This is probably the reason for your duplicates and the reason why the UNION takes such a long time to complete: It processes all generated duplicates and removes them.
So by using a proper join either using ANSI join syntax or using parenthesis you probably
- would get rid of the duplicates
- could use UNION ALL
and performance should be better.
Sample:
SELECT silt.ISIN, 
silt.DESCRIPTION,
sidm1.BUSINESS_DATE, sidm1.AZIONE, sidm1.CAMBIO, sidm1.EMITTENTE, sidm1.OPZIONE, sidm1.PAESE, sidm1.TASSO, sidt1.VAR_TRIMESTRALE, '|' as "END"
FROM SPR_ISIN_LIST_TLX silt
INNER JOIN spr_isin_drm_mi sidm1 on silt.ISIN=sidm1.ISIN
INNER JOIN spr_isin_drm_to sidt1 on silt.ISIN=sidt1.COD_ISIN
where "TYPE"='Bon' or "TYPE"='Equ'
UNION ALL
...or
SELECT silt.ISIN, 
silt.DESCRIPTION,
sidm1.BUSINESS_DATE, sidm1.AZIONE, sidm1.CAMBIO, sidm1.EMITTENTE, sidm1.OPZIONE, sidm1.PAESE, sidm1.TASSO, sidt1.VAR_TRIMESTRALE, '|' as "END"
FROM SPR_ISIN_LIST_TLX silt, spr_isin_drm_mi sidm1, spr_isin_drm_to sidt1
where ("TYPE"='Bon' or "TYPE"='Equ') and silt.ISIN=sidm1.ISIN and silt.ISIN=sidt1.COD_ISIN
UNION
...Regards,
Randolf
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