26h Query. - Mailing list pgsql-general

hi,

I'm having a bit of trouble with my SQL query. It takes about 26h to
run on a 3Ghz PC.  I'd really like to speed this up.

I put this query in a loop to iterate over 20 tables (each table
including summary has 400k records), each time the table name changes.
I this case it's m_alal.  Each table has an identical primary key
ECP_TAG but the RATING column is different.  What I doing is:

Classifying RATING has High, Moderate, Low No Data or Nill.  Then
counting how many tables classify the PK in one of these categories.
This result is kept in my summary table. I end up with a summary table
like:

ECP_CODE | HIGH | MODERATE | LOW ...
M3456         | 3       |     4              | 7      ..

Because I have 20 tables,  if you were to add up along each row it
would sum up to 20.

Anyone have some suggestion on speeding this up.




update public.summary
set
 "MAX_VAL" = CASE
   WHEN public.m_alal."RATING" > public.summary."MAX_VAL" THEN
public.m_alal."RATING"
   ELSE public.summary."MAX_VAL"
   END,
 "MIN_VAL" = CASE
   WHEN public.m_alal."RATING" < public.summary."MIN_VAL" THEN
public.m_alal."RATING"
   ELSE public.summary."MIN_VAL"
   END,
 "NO_DATA" = CASE
   WHEN public.m_alal."RATING" = 0 THEN public.summary."NO_DATA" + 1
   END,
 "NILL" = CASE
   WHEN public.m_alal."RATING" = -1 THEN public.summary."NILL" + 1
   ELSE public.summary."NILL"
   END,
 "HIGH" = CASE
   WHEN public.m_alal."RATING" > 75 THEN public.summary."HIGH" + 1
   ELSE public.summary."HIGH"
   END,
 "MODERATE" = CASE
   WHEN public.m_alal."RATING" > 30 THEN public.summary."MODERATE" + 1
   ELSE public.summary."MODERATE"
   END,
 "LOW" = CASE
   WHEN public.m_alal."RATING" < 25 THEN public.summary."LOW" + 1
   ELSE public.summary."LOW"
   END
 FROM public.m_alal
 WHERE public.summary."ECP_TAG" = public.m_alal."ECP_TAG" AND
 public.m_alal."RATING" IS NOT NULL;