Question about UNION on different databases

Hi,

I have a question.
Maybe you know the answer or suggest a way how I can check it.

I have the following select :

SELECT A,B,C
FROM TABLE_A
UNION ALL
SELECT A,B,C
FROM TABLE_B
UNION ALL
SELECT A,B,C
FROM TABLES_C; where TABLE_A, TABLE_B and TABLE_C - each reside in a different database ( the select is done from a forth database by DB links to the 3 databases )

My question is :

Are the 3 selects in the above select statement executed in PARALLEL ?  i.e - are the selects propagated each to its relevant DB and selects from the remote table together , or is this serialized and how ? If not - is there a way to order the optimizer to parallelize it ? Is there a way to check this ?

Thanks
Orna Received on Wed Nov 07 2001 - 16:55:24 CET