Select MAX issue SQL

Question

Scenario:

I have a table with order status, for example:

/   ORDER    LOG NUMBER   LOG CODE
1   1        1            Preparing
2   1        2            Prepared
3   1        3            Sent
4   2        1            Preparing
5   2        2            Prepared
6   3        1            Preparing

I've been looking for a way to select orders, where last log code is Prepared.

For example I want to see all ORDERS where last LOG CODE is Prepared (last log)

Answer 1

Oracle支持窗口聚合：

group by

或

having

Answer 2

You can use the analytic function to do so

https://docs.oracle.com/cd/B19306_01/server.102/b14200/functions070.htm

It should be something like:

SELECT order LAG(log_code, 1, 0) OVER (PARTITION BY order ORDER BY log_number) AS prev_code FROM orders

This will at least deliver you a resultset which has the last code information.

Instead of using an outer select you should be able to extend the query with

"having prev_code = 'Prepared'"

Answer 3

A pretty efficient way is to use correlated subqueries:

select t.*
from t
where t.lognumber = (select max(t2.lognumber) from t t2 where t.order = t2.order) and
      t.logcode = 'Prepared';