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How to Subtract a Depleting Value from Multiple Rows While Maintaining Cumulative Values?

Linda Hamilton
Release: 2025-01-10 11:55:42
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How to Subtract a Depleting Value from Multiple Rows While Maintaining Cumulative Values?

Subtracting a Depleting Value from Multiple Lots

This problem involves allocating a depleting resource (QuantityConsumed) across multiple inventory lots (Pooled_Lots) while tracking cumulative quantities, remaining demand, and any surplus or deficit.

Data Structures:

We have two tables:

  • Pooled_Lots: Contains details of each inventory lot (Pool, Lot, Quantity).
  • Pool_Consumption: Specifies the total quantity consumed for each pool (PoolId, QuantityConsumed).

Desired Outcome:

The query should generate a result set for each lot in Pooled_Lots, including:

  • Pool, Lot, Quantity, QuantityConsumed, RunningQuantity, RemainingDemand, SurplusOrDeficit.

Solution Approach:

A recursive Common Table Expression (CTE) provides an effective solution. The logic is as follows:

  1. Initialize the CTE with the first lot for each pool.
  2. For subsequent lots within each pool:
    • Update RunningQuantity by subtracting QuantityConsumed if the lot's Quantity exceeds the remaining QuantityConsumed.
    • Calculate RemainingDemand as the difference between QuantityConsumed and the sum of RunningQuantity and the current lot's Quantity.
    • For the last lot in each pool, compute SurplusOrDeficit as the difference between RunningQuantity and RemainingDemand.

SQL Query (Illustrative):

The provided query is incomplete and contains some logical inconsistencies. A robust solution requires careful handling of edge cases (e.g., QuantityConsumed being zero or exceeding the total quantity of all lots in a pool). A corrected and more efficient query would need to be crafted based on a specific database system (e.g., SQL Server, PostgreSQL, MySQL). The following is a conceptual outline of a more accurate approach:

<code class="language-sql">WITH RecursiveCTE AS (
    -- Anchor member: Select the first lot for each pool
    SELECT 
        PL.Pool, PL.Lot, PL.Quantity, PC.QuantityConsumed, 
        PL.Quantity AS RunningQuantity, 
        CASE WHEN PC.QuantityConsumed IS NULL THEN PL.Quantity ELSE PC.QuantityConsumed - PL.Quantity END AS RemainingDemand, 
        0 AS SurplusOrDeficit,
        ROW_NUMBER() OVER (PARTITION BY PL.Pool ORDER BY PL.Lot) as rn
    FROM Pooled_Lots PL
    LEFT JOIN Pool_Consumption PC ON PL.Pool = PC.PoolId
    WHERE PL.Lot = 1 --First lot

    UNION ALL

    -- Recursive member: Process subsequent lots
    SELECT 
        PL.Pool, PL.Lot, PL.Quantity, PC.QuantityConsumed,
        CASE 
            WHEN r.RemainingDemand > PL.Quantity THEN r.RunningQuantity - PL.Quantity
            ELSE r.RunningQuantity - r.RemainingDemand
        END AS RunningQuantity,
        CASE 
            WHEN r.RemainingDemand > PL.Quantity THEN r.RemainingDemand - PL.Quantity
            ELSE 0
        END AS RemainingDemand,
        CASE WHEN r.rn = (SELECT MAX(rn) FROM RecursiveCTE WHERE Pool = PL.Pool) THEN r.RunningQuantity - r.RemainingDemand ELSE 0 END AS SurplusOrDeficit,
        r.rn + 1
    FROM Pooled_Lots PL
    INNER JOIN RecursiveCTE r ON PL.Pool = r.Pool AND PL.Lot = r.rn + 1
    LEFT JOIN Pool_Consumption PC ON PL.Pool = PC.PoolId
)
SELECT * FROM RecursiveCTE
ORDER BY Pool, Lot;</code>
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Results:

The output will show each lot's details, including the cumulative RunningQuantity, the remaining RemainingDemand, and any SurplusOrDeficit after allocation. The accuracy of the RunningQuantity, RemainingDemand, and SurplusOrDeficit calculations depends on the precise logic implemented in the recursive CTE to handle all possible scenarios. A complete and tested solution would require knowing the specific database system and potentially sample data for validation.

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