SQL - find missing records in each date - sql

Question

I have two tables:
A product table that has productID of all products (productName, productID)
A transaction table of records with columns: date (for last 3 months) and productID. All productID should have at least one record for each date.
However, there are missing productID records for some datss, and I would like to find the missing productID and the respective dates they are missing from.
Right now, I'm only able to find missing records for one particular date, which is:
Select productName, productID
from product a inner join transaction b
On a.productid=b.productid
Where a.productid not in
(
Select distinct productid
From transaction
Where date='2019-03-01'
)
I would like to have a table that consolidates all dates and their respective missing productid records. How can I proceed from here?
create table product
(ProductID INT,
ProductName Char (30)
);
insert into product values
(1, 'apple'),
(2, 'orange'),
(3, 'pear');
create table transaction1
(transDate Date,
productID INT,
revenue FLOAT);
insert into transaction1 values
('2019-03-01', 1, 2.5),
('2019-03-01', 2, 4.0),
('2019-03-01', 2, 8.0),
('2019-03-01', 3, 6.0),
('2019-03-02', 1, 7.0),
('2019-03-02', 3, 14.0),
('2019-03-03', 1, 1.5) ;
What i have will be similar to this, where productID=2 is missing from 03-02. I am working for dates from beginning of the year till yesterday, which are all recorded in the transaction table.
#SimonPrice

Answer 1

The most tricky part of your problem is to generate the list of all dates for your expected date which is 90 days in your case. Here I have created all dates using a loop. One additional column 'Common' added with value 1 to Product and Temp table to join with the product table for all date and all product.
Note: Just change the value of #HowManyDay as per days you wants to check.
DECLARE #HowManyDay INT
SET #HowManyDay = 8
DECLARE #LoopCount INT
SET #LoopCount = 0
DECLARE #TempTable TABLE(Common INT,All_Date DATE)
WHILE #LoopCount <= #HowManyDay-1
BEGIN
INSERT INTO #TempTable (Common,All_Date)
VALUES (1,DATEADD(DD,-#LoopCount,GETDATE()))
SET #LoopCount = #LoopCount + 1
END
SELECT B.All_Date,C.productID,C.productName,T.date
FROM #TempTable B
INNER JOIN
(
SELECT 1 [Common],*
FROM product
)C ON B.Common = C.Common
LEFT JOIN transaction_details T ON C.productID = T.productID AND B.All_Date = T.date
WHERE T.date IS NULL
ORDER BY 3 ASC,1 DESC