Using aggregation function to filter record based on MIN timestamp

问题

SELECT * FROM ABC_CUSTOMER_DETAILS abc_detail
INNER JOIN ABC_CUSTOMERS abc_cust
ON abc_detail.ID=abc_cust.CUSTOMER_ID
WHERE abc_detail.COUNTRY_CODE='KE'
AND CREATION_TIMESTAMP=(SELECT MIN (CREATION_TIMESTAMP)
                        FROM ABC_CUSTOMER_DETAILS abc_detail
                        INNER JOIN ABC_CUSTOMERS abc_cust
                        ON abc_detail.ID=abc_cust.CUSTOMER_ID
                        WHERE abc_detail.COUNTRY_CODE='KE');

Above script query join record from ABC_CUSTOMER_DETAILS to ABC_CUSTOMERS nd select thw one with earliest timestamp.

Anyway if I able not to repeat the same JOIN and WHERE clause in CREATION_TIMESTAMP condition?

回答1:

There are several ways to get the earliest record and to avoid having to type the same criteria twice.

Using FETCH FIRST ROWS (available as of Oracle 12c)

select * 
from abc_customer_details cd
join abc_customers c on c.id = cd.customer_id
where cd.country_code = 'KE'
order by creation_timestamp
fetch first row only;

Using a CTE (WITH clause)

with cte as
(
  select * 
  from abc_customer_details cd
  join abc_customers c on c.id = cd.customer_id
  where cd.country_code = 'KE'
)
select *
from cte
where (creation_timestamp) = (select min(creation_timestamp) from cte);

Using window functions

select *
from
(
  select cd.*, c.*, min(creation_timestamp) over () as min_creation_timestamp
  from abc_customer_details cd
  join abc_customers c on c.id = cd.customer_id
  where cd.country_code = 'KE'
)
where creation_timestamp = min_creation_timestamp;

(I changed the join criteria in all these queries, by the way. It just does seem extremely unlikely you want to join on abc_customer_details.id = abc_customers.customer_id.)

回答2:

You could make use of MIN() analytic function.

SELECT
    *
FROM
    (
        SELECT
            abc_detail.*,
            abc_cust.*,
            MIN(creation_timestamp) OVER(
                PARTITION BY abc_detail.id
            ) AS min_timestamp
        FROM
            abc_customer_details abc_detail
            INNER JOIN abc_customers abc_cust
        ON abc_detail.id = abc_cust.customer_id
        WHERE
            abc_detail.country_code = 'KE'
    )
WHERE
    creation_timestamp = min_timestamp;

来源：https://stackoverflow.com/questions/50461060/using-aggregation-function-to-filter-record-based-on-min-timestamp

标签

Oracle

join

aggregate-functions

min