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:
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:
RunningQuantity
by subtracting QuantityConsumed
if the lot's Quantity
exceeds the remaining QuantityConsumed
.RemainingDemand
as the difference between QuantityConsumed
and the sum of RunningQuantity
and the current lot's Quantity
.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>
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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