title: Select from several partitions at once
body: <p>Excuse me for my english. 
  I have 2 tables, both partitioned by date interval, but on different fields.
  There is a big amount of records in both tables(~100kk in each partition).
  First table keep it's 3 last(by date) partitions in fast discks tablespace, others partitions is in slow discks tablespace.
  Also I have some system, which processing data. It execute processes in parallel, each one get data from first table by select statement and put processed data into second table. 
  So I need select data from first table only from "fast"(!) partitions to put it in second table.
  But second table partitioned on other(date too) field. And when processes executing in parallel I get deadlocks when different processes trying to put data into the same partition in 2nd table.</p>
  
  <p>Good solution is for each process take data from only "fast" partitions(but all of them in one time) only data for one partition in 2nd table. In this case each process will push data in one partition. But I don't have any idea how to do it.</p>
  
  <p>If I make </p>
  
  <pre><code>select t.field1, t.field2 from (select * from FIRST_TABLE partition("P1") union all
  select * from FIRST_TABLE partition("P2") union all
  select * from FIRST_TABLE partition("P3")) t
  where t.field3='someVal' --Indexed field in FIRST_TABLE 
  </code></pre>
  
  <p>will OracleDB use local indexes on partitions in FIRST_TABLE to resolve where-clause? How will this way affect the performance? </p>
  
  <p>Any ideas to solve my problem?</p>
  
  <p>PS It's a lot of questions about how to select data from several partitions in one select-statement, but I didn't found answer usefull for my situation. </p>