How to Merge SQL Tables and Guarantee Unique Date Values?

Merging Tables and Ensuring Unique Date Values in SQL

To merge two tables while ensuring the uniqueness of date values, utilize the following approach:

1. Union All Two Subqueries: Create two subqueries to extract data from the Inbound and Outbound tables. Sum the Quantity column in the Inbound subquery and count the OutboundType in the Outbound subquery.
2. Combine Results with Union All: Combine the results of both subqueries using the UNION ALL operator. This will create a single result set containing both inbound and outbound transactions.
3. Group by Date and Product: Apply the GROUP BY operator to the combined result set, using the Date and Product columns as grouping criteria. This will ensure that each unique date-product combination is represented only once in the final result.
4. Sum Inbound and Outbound: Use SUM to calculate the total Inbound quantity for each date-product combination and SUM to count the total Outbound transactions for each combination.
5. Display Results: The final result set will display the Date, Product, total Inbound quantity, and total Outbound transactions for each unique date and product combination.

Example Code:

SELECT Date, Product, SUM(Inbound) AS Inbound, SUM(Outbound) AS Outbound
FROM ((SELECT Inbound_Date AS Date, Product, SUM(Quantity) AS Inbound, 0 AS Outbound
      FROM Inbound
      GROUP BY 1, 2
     ) UNION ALL
     (SELECT Outbound_Date, Product, 0 AS Inbound, COUNT(*) AS Outbound
      FROM Outbound
      GROUP BY 1, 2
     )
    ) io
GROUP BY Date, Product;

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