You have a table MonthlySales with columns Store, Jan, Feb, Mar representing sales per month. You want to create a report listing Store, Month, Sales rows. Which SQL approach correctly unpivots this data?
AUse UNPIVOT: <code>SELECT Store, Month, Sales FROM MonthlySales UNPIVOT (Sales FOR Month IN ([Jan], [Feb], [Mar])) AS Unpvt;</code>
BUse PIVOT: <code>SELECT Store, Month, Sales FROM MonthlySales PIVOT (SUM(Sales) FOR Month IN ([Jan], [Feb], [Mar])) AS Pvt;</code>
CUse JOIN to combine Jan, Feb, Mar columns into rows
DUse GROUP BY Store, Month without unpivot
Step-by-Step Solution
Solution:
Step 1: Identify the goal
We want to transform columns Jan, Feb, Mar into rows with Month and Sales columns.
Step 2: Choose correct SQL operation
UNPIVOT converts columns into rows; Use UNPIVOT: SELECT Store, Month, Sales FROM MonthlySales UNPIVOT (Sales FOR Month IN ([Jan], [Feb], [Mar])) AS Unpvt; uses correct syntax for this.
Step 3: Evaluate other options
PIVOT aggregates rows into columns (wrong direction), JOIN is complex and unnecessary, GROUP BY alone doesn't reshape columns.
Final Answer:
Use UNPIVOT: SELECT Store, Month, Sales FROM MonthlySales UNPIVOT (Sales FOR Month IN ([Jan], [Feb], [Mar])) AS Unpvt; -> Option A
Quick Check:
Unpivot columns to rows = Use UNPIVOT: SELECT Store, Month, Sales FROM MonthlySales UNPIVOT (Sales FOR Month IN ([Jan], [Feb], [Mar])) AS Unpvt; [OK]
Quick Trick:Unpivot columns to rows using UNPIVOT with FOR and IN [OK]
Common Mistakes:
Using PIVOT instead of UNPIVOT
Trying to reshape with GROUP BY only
Overcomplicating with JOINs
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