Which is faster: 2 selects or 1 union
Hello,
I have 2 tables... each with 500,000 records each. Each table
has about 15 columns. Each has a non unique index, because
there can be multiple records with the same index.
I AM USING PL/SQL.
The union goes something like this:
SELECT tblA.*, tblB.*
FROM tblA, tblB,
WHERE A.ID (+)= B.ID
UNION
SELECT tblA.*, tblB.*
FROM tblA, tblB,
WHERE B.ID (+)= A.ID
I want all records and fields from table A that are not in table
B and vice versa.
NOW THE QUESTION...
Is it faster to do this union or just perform 2 select
statements and use logic to get the results I am looking for.
thanks for your help or other ideas!
larry
null
Hi Larry
<<I want all records and fields from table A that are not
in table B and vice versa.>>
Try this,
Select *
from tbl a
where not exists (select 'x'
from tbl b
where b.id = a.id)
union
select *
from tbl b
where not exists (select 'x'
from tbl a
where a.id = b.id)
This would be faster.
-Raj
larry (guest) wrote:
: Hello,
: I have 2 tables... each with 500,000 records each. Each table
: has about 15 columns. Each has a non unique index, because
: there can be multiple records with the same index.
: I AM USING PL/SQL.
: The union goes something like this:
: SELECT tblA.*, tblB.*
: FROM tblA, tblB,
: WHERE A.ID (+)= B.ID
: UNION
: SELECT tblA.*, tblB.*
: FROM tblA, tblB,
: WHERE B.ID (+)= A.ID
: I want all records and fields from table A that are not in
table
: B and vice versa.
: NOW THE QUESTION...
: Is it faster to do this union or just perform 2 select
: statements and use logic to get the results I am looking for.
: thanks for your help or other ideas!
: larry
null
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