Sample Records, need ideas, Fill Table SQL samples

Question

Say that I need to select 500 records of the berst quality for a Store number 77, by some Spend column, say it is: SPEND_12_MONTHS
I picked say 45 records/rows from this one Table, and I need to fill the other 455 on the spend column from a 2nd Table,
how would I do that ?
Just looking for general ideas, so I have no Sample of code to show, but the rows would be Distinct with no duplicates
on the Customer_id (primary key).
I have a need to do this on a handful of Stores, not just 1, but trying to get an idea, so for example:
Store | Primary Table 1 | Fill Table 2
1-----------45--------------------------455
2-----------23--------------------------477
3-----------11--------------------------489
The reason why I need to pull from the First Table is that it has Priority #1, and Table 2, Priority #2. In Table #1 there isn't that many records, so that's why I need to fill from Table 2.
Thank You!
Am on Oracle 10G R2

Answer 1

I am not sure if I get you correctly.
You have:
table1 Top Prio Customers (small number)
table2 All Customers.
now you want to query all 500 customers preferable from table1 if they exist there otherwise from table2. The Customer_ID is unique in each table and consitent in both tables.
Right?
There are many ways...
SELECT t1.*
from table1 t1
UNION ALL
SELECT t2.*
from table2 t2
left join table1 t1
on t1.Customer_id = t2.Customer_id
where  t1.Customer_id is NULL;You can also use NOT EXISTS not this LEFT trick works quite fast in all ORACLE versions, but for 500 rows, who cares.