populating table from different tables - sql

Question

Good day.
I have the following tables:
Order_Header(Order_id {pk}, customer_id {fk}, agent_id {fk}, Order_date(DATE FORMAT))
Invoice_Header (Invoice_ID {pk}, Customer_ID {fk}, Agent_ID{fk}, invoice_Date{DATE FORMAT} )
Stock( Product_ID {pk}, Product_description)
I created a table called AVG_COMPLETION_TIME_FACT and want to populate it with the following values regarding the previous 3 tables:
Product_ID
Invoice_month
Invoice_Year
AVG_Completion_Time (Invoice_date - Order_date)
I have the following code that doesn't work:
INSERT INTO AVG_COMPLETION_TIME_FACT(
SELECT PRODUCT_ID, EXTRACT (YEAR FROM INVOICE_DATE), EXTRACT (MONTH FROM INVOICE_DATE), (INVOICE_DATE - ORDER_DATE)
FROM STOCK, INVOICE_HEADER, ORDER_HEADER
GROUP BY PRODUCT_ID, EXTRACT (YEAR FROM INVOICE_DATE), EXTRACT (MONTH FROM INVOICE_DATE)
);
I want to group it by the product_id, year of invoice and month of invoice.
Is this possible?
Any advice would be much appreciated.
Regards

Answer 1

Short answer: it may be possible - if your database contains some more columns that are needed for writing the correct query.
There are several problems, apart from the syntactical ones. When we create some test tables, you can see that the answer you are looking for cannot be derived from the columns you have provided in your question. Example tables (Oracle 12c), all PK/FK constraints omitted:
-- 3 tables, similar to the ones described in your question,
-- including some test data
create table order_header (id, customer_id, agent_id, order_date )
as
select 1000, 100, 1, date'2018-01-01' from dual union all
select 1001, 100, 2, date'2018-01-02' from dual union all
select 1002, 100, 3, date'2018-01-03' from dual
;
create table invoice_header ( id, customer_id, agent_id, invoice_date )
as
select 2000, 100, 1, date'2018-02-01' from dual union all
select 2001, 100, 2, date'2018-03-11' from dual union all
select 2002, 100, 3, date'2018-04-21' from dual
;
create table stock( product_id, product_description)
as
select 3000, 'product3000' from dual union all
select 3001, 'product3001' from dual union all
select 3002, 'product3002' from dual
;
If you join the tables as you have done it (using a cross join), you will see that you get more rows than expected ... But: Neither the invoice_header table, nor the order_header table contains any PRODUCT_ID data. Thus, we cannot tell which product_ids are associated with the stored order_ids or invoice_ids.
select
product_id
, extract( year from invoice_date )
, extract( month from invoice_date )
, invoice_date - order_date
from stock, invoice_header, order_header -- cross join -> too many rows in the resultset!
-- group by ...
;
...
27 rows selected.
For getting your query right, you should probably write INNER JOINs and conditions (keyword: ON). If we try to do this with your original table definitions (as provided in your question) you will see that we cannot join all 3 tables, as they do not contain all the columns needed: PRODUCT_ID (table STOCK) cannot be associated with ORDER_HEADER or INVOICE_HEADER.
One column that these 2 tables (ORDER_HEADER and INVOICE_HEADER) do have in common is: customer_id, but that's not enough for answering your question. However, we can use it for demonstrating how you could code the JOINs.
select
-- product_id
IH.customer_id as cust_id
, OH.id as OH_id
, IH.id as IH_id
, extract( year from invoice_date ) as year_
, extract( month from invoice_date ) as month_
, invoice_date - order_date as completion_time
from invoice_header IH
join order_header OH on IH.customer_id = OH.customer_id
-- the stock table cannot be joined at this stage
;
Missing columns:
Please regard the following just as "proof of concept" code. Assuming that somewhere in your database, you have tables that have columns that {1} link STOCK and ORDER_HEADER (name here: STOCK_ORDER) and {2} link ORDER_HEADER and INVOICE_HEADER (name here: ORDER_INVOICE), you could actually get the information you want.
-- each ORDER_HEADER is mapped to multiple product_ids
create table stock_order
as
select S.product_id, OH.id as oh_id -- STOCK and ORDER_HEADER
from stock S, order_header OH ; -- cross join, we use all possible combinations here
select oh_id, product_id
from stock_order
order by OH_id
;
PRODUCT_ID OH_ID
---------- ----------
3000 1000
3000 1001
3000 1002
3001 1000
3001 1001
3001 1002
3002 1000
3002 1001
3002 1002
9 rows selected.
-- each INVOICE_HEADER mapped to a single ORDER_HEADER
create table order_invoice ( order_id, invoice_id )
as
select 1000, 2000 from dual union all
select 1001, 2001 from dual union all
select 1002, 2002 from dual
;
For querying, make sure that you code the correct JOIN conditions (ON ...) eg
-- example query. NOTICE: conditions in ON ...
select
S.product_id
, IH.customer_id as cust_id
, OH.id as OH_id
, IH.id as IH_id
, extract( year from invoice_date ) as year_
, extract( month from invoice_date ) as month_
, invoice_date - order_date as completion_time
from invoice_header IH
join order_invoice OI on IH.id = OI.invoice_id -- <- new "link" table
join order_header OH on OI.order_id = OH.id
join stock_order SO on OH.id = SO.OH_id -- <- new "link" table
join stock S on S.product_id = SO.product_id
;
Now you can add the GROUP BY, and SELECT only the columns you need. Combined with an INSERT, you should write something like ...
-- example avg_completion_time_fact table.
create table avg_completion_time_fact (
product_id number
, year_ number
, month_ number
, avg_completion_time number
) ;
insert into avg_completion_time_fact ( product_id, year_, month_, avg_completion_time )
select
S.product_id
, extract( year from invoice_date ) as year_
, extract( month from invoice_date ) as month_
, avg( invoice_date - order_date ) as avg_completion_time
from invoice_header IH
join order_invoice OI on IH.id = OI.invoice_id
join order_header OH on OI.order_id = OH.id
join stock_order SO on OH.id = SO.OH_id
join stock S on S.product_id = SO.product_id
group by S.product_id, extract( year from invoice_date ), extract( month from invoice_date )
;
The AVG_COMPLETION_TIME_FACT table now contains:
SQL> select * from avg_completion_time_fact order by product_id ;
PRODUCT_ID YEAR_ MONTH_ AVG_COMPLETION_TIME
---------- ---------- ---------- -------------------
3000 2018 3 68
3000 2018 4 108
3000 2018 2 31
3001 2018 3 68
3001 2018 2 31
3001 2018 4 108
3002 2018 3 68
3002 2018 4 108
3002 2018 2 31
It is not completely clear what the final query for your database (or schema) will look like, as we don't know the definitions of all the tables it contains. However, if you apply the techniques and stick to the syntax of the examples, you should be able to obtain the required results. Best of luck!