Temporary tables in Packages - Oracle - performance

Question

I am kind of new in Oracle.
I am trying to create a package that has several functions.
This is the pseudocode of what I want to do
function FunctionA(UserID, startdate, enddate)
/* Select TransactionDate, Amount
from TableA
where TransactionDate between startdate and enddate
and TableA.UserID = UserID */
Return TransactionDate, Amount
end FunctionA
function FunctionB(UserID, startdate, enddate)
/* Select TransactionDate, Amount
from TableB
where TransactionDate between startdate and enddate
and TableB.UserID = UserID */
Return TransactionDate, Amount
end FunctionA
TYPE TRANSACTION_REC IS RECORD(
TransactionDate DATE,
TransactionAmt NUMBER);
function MainFunction(startdate, enddate)
return TBL
is
vTrans TRANSACTION_REC;
begin
FOR rec IN
( Select UserID, UserName, UserStatus
from UserTable
where EntryDate between startdate and enddate )
LOOP
vTrans := FunctionA(rec.UserID, startdate, enddate)
if vTrans.TransactionDate is null then
vTrans := FunctionB(rec.UserID, startdate, enddate)
if vTrans.TransactionDate is null then
rec.UserStatus := 'Inactive'
endif;
endif;
END Loop;
PIPE ROW(USER_OBJ_TYPE(rec.UserID,
rec.UserName,
rec.UserStatus,
vTrans.TransactionDate,
vTtans.TransactionAmt));
end MainFunction
Running this kind of code takes a long time because TableA and TableB is a very large table, and I am only getting 1 entry per record from the tables.
I would want to create a temporary table (TempTableA, TempTableB) within the package that will temporarily store all records based on the startdate and enddate, so that when I try to retrieve the TransactionDate and Amount for each rec, I will only refer to the TempTables (which is smaller than TableA and TableB).
I also want to take into consideration if the UserID is not found in TableA and TableB. So basically, when there are no records found in TableA and TableB, I also want the entry in the output, but it is indicated that the user is inactive.
Thank you for all your help.

Answer 1

SQL is a set-based language. It is far more efficient to execute one statement which returns all the rows you need than to execute many statements which each return a single row.
Here is one way of getting all your rows at once. It uses a common table expression because you read the whole of the UserTable and you should only do that once.
with cte as
(select UserID
, UserStatus
from UserTable )
select cte.UserID
, cte.UserStatus
, TableA.TransactionDate
, TableA.Amount
from cte join TableA
on (cte.UserID = TableA.UserID)
where cte.UserStatus = 'A'
and TableA.TransactionDate between startdate and enddate
union
select cte.UserID
, cte.UserStatus
, TableB.TransactionDate
, TableB.Amount
from cte join TableB
on (cte.UserID = TableB.UserID)
where cte.UserStatus != 'A'
and TableB.TransactionDate between startdate and enddate
By the way, be careful with temporary tables. They aren't like temporary tables in T-SQL. They are permanent heap tables, it's just their data that's temporary. This means that populating a temporary table is an expensive process, because the database writes all those rows to disk. Consequently we need to be certain that the performance gain we get by reading a dataset from a temporary table is worth the overhead of all those writes.
That certainly would not be the case with your code. In fact, it is really pretty rare that the answer to a performance question turns out to be "Use a Global Temporary Table", at least not in Oracle. Better queries are the way to go, and in particular, embracing the Joy of Sets!

Answer 2

Probably better to do it in one query, e.g.:
Select UserTable.UserID, UserTable.UserName, UserTable.UserStatus
,TableA.TransactionDate AS ATransactionDate
,TableA.Amount AS AAmount
,TableB.TransactionDate AS BTransactionDate
,TableB.Amount AS BAmount
from UserTable
left join TableA
on (UserTable.UserID = TableA.UserID)
left join TableB
on (UserTable.UserID = TableB.UserID)
where UserTable.EntryDate between startdate and enddate