80. Two-Dimensional Pivot: Store by Quarter
A two-dimensional pivot groups by one dimension on the rows and spreads a second dimension across the columns. Here each row is a store and each column is a quarter, with summed units in the cells.
Task: the sales2d table has one row per store per quarter per product (multiple products per store-quarter). Pivot to one row per store with the total units sold in each quarter as columns q1..q4. Return store, q1, q2, q3, q4. Use SUM(CASE WHEN quarter='Qx' THEN units END) so multiple product rows in the same store-quarter are added together. Order by store.
Output columns, in order: store, q1, q2, q3, q4.
This is the result for the example data above. On Submit your query is graded against this example plus 4 hidden edge cases — 5test cases in all. A sloppy query that only fits the example won't pass.