Oracle Loop Through Join Statement

问题

I need to execute a statement in PL-SQL that taking a selection of Ids, executes a join against a sub-set of those ids... in the example below i have about 700000 customers, and a far more complex query than shown here in the simple while loop in this example...i'm seeding quite poor performance and am curious if chopping up my current PL-SQL into 'chunks' would yield a perf increase?

Currently:

declare
  TYPE customerIdTabType IS TABLE OF customer.CustomerId%TYPE INDEX BY BINARY_INTEGER;
  vars customerIdTabType;

  -- maybe this should be in a table?
  cursor c is
  select
      c.CustomerId
  from customer c
  join productcustomers pc on pc.customerid = c.customerid
  join product p on p.productid = pc.productid
  where
      c.CustomerId > 1000;

begin  
  open c;
  loop
  fetch c bulk collect into vars limit 1000;

  -- here is where instead of looping through each item in vars
  -- i actually want to 'join' to the 1000 that i have.  
  forall i in 1..vars.count
  insert into xxx (CustomerId) 
  values (vars(i));
  commit;

  exit when vars.count = 0;
  end loop;
  close c;

end;

1. Select a list of CustomerIds into a "temporary" storage container - not sure what the options are?
2. Process those CustomerIds in batches of say... 1000 by joining them to another query
3. Insert all results into a physical table

so, in T-SQL might be..

-- create a temp table
create table #MyTempTable (
    id int identity(1,1)
    ,customerid varchar(10)
)

-- populate that table
insert into #MyTempTable
select Customerid 
from schema.Customers

-- create some vars for looping
declare i int, c int;
select i = 0;
select c = count(*) from #MyTempTable;

-- loop through the original set in 'chunks' of 1000​
while i < c
begin
    insert into SomeOtherTable
        (CustomerId, CustomerAttribute)
    select
        o.CustomerId
        ,o.CustomerAttribute
    from OtherTable o
    join #MyTempTable t
    on o.CustomerId = t.CustomerId
    where
        t.Id between i and i+1000    -- from 0 to 1000

    set @i = i+1000    ​-- next loop will be from 1000 to 2000
end

Thanks

回答1:

Then, what about this

select startid = min(id) from customer;
select maxid = max(id) from customer;

i = startid
while i <= maxid

begin
   with myCTE as (select ... from customer where id >= i and id < i + 1000)
   insert into xxx (....)
   select ....
   from myCustomerChunk
        join productcustomers pc on ....
        join product p on ....

   i = i+1000
end

That avoids doing all 700000 inserts in one statement which is what was probably grinding down your query... and the cursor made things just worse. PS: this is a hodge-podge of pseudo and actual code, so you will have to work out the real syntax.

回答2:

Both cursors and temp tables are poor solutions here. But cursors are the worse of the two. A CTE (Common Table Expression) would be a better solution, but even that is not necessary here. Why not just use a straight insert into... select statement from the get-go

Insert into xxx (CustomerId)
select
    c.CustomerId
from customer c
     join productcustomers pc on pc.customerid = c.customerid
     join product p on p.productid = pc.productid
where
    c.CustomerId > 1000;

If you do need to break it up, do not use a cursor or a temp table. I expect a CTE would be a better solution.

来源：https://stackoverflow.com/questions/29968879/oracle-loop-through-join-statement