根据顺序选择多个记录

Question

i have a table with a bunch of customer IDs. in a customer table is also these IDs but each id can be on multiple records for the same customer. i want to select the most recently used record which i can get by doing order by <my_field> desc

say i have 100 customer IDs in this table and in the customers table there is 120 records with these IDs (some are duplicates). how can i apply my order by condition to only get the most recent matching records?

dbms is sql server 2000.

table is basically like this: loc_nbr and cust_nbr are primary keys

a customer shops at location 1. they get assigned loc_nbr = 1 and cust_nbr = 1 then a customer_id of 1.

they shop again but this time at location 2. so they get assigned loc_nbr = 2 and cust_Nbr = 1. then the same customer_id of 1 based on their other attributes like name and address.

because they shopped at location 2 AFTER location 1, it will have a more recent rec_alt_ts value, which is the record i would want to retrieve.

Answer 1

Use an aggregate function in the query to group by customer IDs:

  SELECT cust_Nbr, MAX(rec_alt_ts) AS most_recent_transaction, other_fields
    FROM tableName
GROUP BY cust_Nbr, other_fields
ORDER BY cust_Nbr DESC;

This assumes that rec_alt_ts increases every time, thus the max entry for that cust_Nbr would be the most recent entry.

Answer 2

Since you didn't give real table and field names, this is just psuedo code for a solution.

select * 
from customer_table t2
inner join location_table t1 
  on t1.some_key = t2.some_key
where t1.LocationKey = (select top 1 (LocationKey) as LatestLocationKey from  location_table  where cust_id = t1.cust_id order by some_field)

Answer 3

You want to use the ROW_NUMBER() function with a Common Table Expression (CTE).

Here's a basic example. You should be able to use a similar query with your data.

;WITH TheLatest AS
(
    SELECT *, ROW_NUMBER() OVER (PARTITION BY group-by-fields ORDER BY sorting-fields) AS ItemCount 
    FROM TheTable 
)
SELECT * 
FROM TheLatest 
WHERE ItemCount = 1

UPDATE: I just noticed that this was tagged with sql-server-2000. This will only work on SQL Server 2005 and later.

Answer 4

By using time and date we can take out the recent detail for the customer. use the column from where you take out the date and the time for the customer.

eg:

SQL> select ename , to_date(hiredate,'dd-mm-yyyy hh24:mi:ss') from emp order by to_date(hiredate,'dd-mm-yyyy hh24:mi:ss');