Oracle SQL使用变量分区名称

Question

I run a daily report that has to query another table which is updated separately. Due to the high volume of records in the source table (8M+ per day) each day is stored in it's own partition. The partition has a standard format as P ... 4 digit year ... 2 digit month ... 2 digit date , so yesterday's partition is P20140907 .

At the moment I use this expression, but have to manually change the name of the partition each day:

select * from <source_table> partition (P20140907) where ....

By using sysdate , toChar and Concat I have created another table called P_NAME2 that will automatically generate and update a string value as the name of the partition that I need to read. Now I need to update my main query so it does this:

select * from <source_table> partition (<string from P_NAME2>) where ....

Answer 1

You are working too hard. Oracle already does all these things for you. If you query the table using the correct date range oracle will perform the operation only on the relevant partitions - this is called pruning .

I suggest reading the docs on that.

If you'r still skeptic, Query all_tab_partitions.HIGH_VALUE to get each partitions high value (the table you created ... ).

Answer 2

I thought I'd pop back to share how I solved this in the end. The source database has a habit of leaking dates across partitions which is why queries for one day were going outside a single partition. I can't affect this, just work around it ...

begin    
execute immediate 
'create table LL_TEST as
select *
from SCHEMA.TABLE Partition(P'||TO_CHAR(sysdate,'YYYYMMDD')||')
where COLUMN_A=''Something''
and COLUMN_B=''Something Else''
';
end
;

Using the PL/SQL script I create the partition name with TO_CHAR(sysdate,'YYYYMMDD') and concatenate the rest of the query around it.

Note that the values you are searching for in the where clause require double apostrophes so to send 'Something' to the query you need ''Something'' in the script.

It may not be pretty, but it works on the database that I have to use.