PG is creating the union of January, February and March tables first and that doesn't have an index on it.  If you're going to do many queries using the union of those three tables, you might want to place their contents into one table and create an index on it.

Otherwise, try something like this:

SELECT "Rut Cliente"
FROM "Internet_Abril"
WHERE "Rut Cliente"  NOT IN (SELECT "Rut Cliente"  FROM
AND "Rut Cliente" NOT IN (SELECT "Rut Cliente"  FROM
AND "Rut Cliente" NOT IN (SELECT "Rut Cliente"  FROM

You could also compare the performance of that to this and choose the one that works the best:

SELECT "Rut Cliente"
FROM "Internet_Abril" a
LEFT JOIN "Internet_Enero" e ON a."Rut Cliente" = e."Rut Cliente"
LEFT JOIN "Internet_Febrero" f ON a."Rut Cliente" = f."Rut Cliente"
LEFT JOIN "Internet_Marzo" m ON a."Rut Cliente" = m."Rut Cliente"
WHERE e."Rut Cliente" IS NULL AND f."Rut Cliente" IS NULL and m."Rut Cliente" IS NULL;


On 9/7/05, Christian Compagnon <[EMAIL PROTECTED]> wrote:

I'm a newbie in postgresql, I've installed it on a Windows XP machine
( I can't use linux, it's a company machine ), I'm courious why this
query takes so long

SELECT "Rut Cliente"
FROM "Internet_Abril"
WHERE "Rut Cliente"  NOT IN ((SELECT "Rut Cliente"  FROM
"Internet_Enero") UNION (SELECT "Rut Cliente"  FROM
"Internet_Febrero") UNION (SELECT "Rut Cliente"  FROM

it takes about 100 minutes to complete the query.
All tables has index created ( Rut Cliente is a VarChar ), and tables
has 50.000 records each.

The explain for the query tells the following

Seq Scan on "Internet_Abril"  (cost=19406.67..62126112.70 rows=24731 width=13)
  Filter: (NOT (subplan))
       ->  Materialize  (cost=19406.67..21576.07 rows=136740 width=13)
        ->  Unique  (cost=17784.23..18467.93 rows=136740 width=13)
        ->  Sort  (cost=17784.23..18126.08 rows=136740 width=13)
Key: "Rut Cliente"
          ->  Append  (cost=0.00..3741.80 rows=136740 width=13)
          ->  Subquery Scan "*SELECT* 1"  (cost=0.00..1233.38
rows=45069 width=13)
           ->  Seq Scan on "Internet_Enero"  (cost=0.00..782.69
rows=45069 width=13)
           ->  Subquery Scan "*SELECT* 2"  (cost=0.00..1104.06
rows=40353 width=13)
             ->  Seq Scan on "Internet_Febrero"  (cost=0.00..700.53
rows=40353 width=13)
           ->  Subquery Scan "*SELECT* 3"  (cost=0.00..1404.36
rows=51318 width=13)
            ->  Seq Scan on "Internet_Marzo"  (cost=0.00..891.18
rows=51318 width=13)

Any help will be apreciated, It's for my thesis


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