Joining tables with recent date for each row then weighted averaging - sql

Question

There are three tables, such as equip_type , output_history, and time_history in Oracle DB.
Is there a way to join the three tables as shown below at (1) and then to get weighted average as shown below at (2)?
--equip_type table and the date
CREATE TABLE equip_type (
EQUIP_TYPE VARCHAR(60),
EQUIP VARCHAR(60)
);
INSERT INTO equip_type VALUES ('A','e1');
-- output_history and data
CREATE TABLE output_history (
EQUIP VARCHAR(60),
MODEL VARCHAR(60),
Data1 VARCHAR(60),
QUANTITY NUMBER(10)
);
INSERT INTO output_history VALUES ('e1','m1','20180103',10);
INSERT INTO output_history VALUES ('e1','m1','20180106',20);
--time_history table and data
CREATE TABLE time_history (
EQUIP VARCHAR(60),
MODEL VARCHAR(60),
Data2 VARCHAR(60),
time NUMBER(10)
);
INSERT INTO time_history VALUES ('e1','m1','20180101',6);
INSERT INTO time_history VALUES ('e1','m1','20180105',5);
(1) How to get joined table as below?
EQUIP MODEL DATE1 QUANTITY DATE2 TIME TYPE
---- ---- ---------- ------ -------- ---- ----
e1 m1 20180103 10 20180101 6 A
e1 m1 20180106 20 20180105 5 A
For each row in OUTPUT_HISTORY, *the most recent row at the point of the DATE1*in TIME_HISTORY is joined.
(2) Then, With the joined table above, how to get weighted average of TIME?
(QUANTITY * TIME) / sum of QUANTITY group by TYPE, MODEL
for example,(10×6 + 20×5)÷(10+20) for equip type A and model m1

Answer 1

One method uses analytic functions to get the most recent record and then simple aggregation
select sum(quantity * time) / sum(quantity)
from output_history oh left join
(select th.*,
row_number() over (partition by equip, model order by date2 desc) as seqnum
from time_history th
) th
on oh.equip = th.equip and oh.model = th.model and th.seqnum = 1
group by equip, model;