国外版

算法题（国外版）/rearrange-products-table.html

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+<p>Table: <code>Products</code></p>
+
+<pre>
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| product_id  | int     |
+| store1      | int     |
+| store2      | int     |
+| store3      | int     |
++-------------+---------+
+product_id is the primary key for this table.
+Each row in this table indicates the product&#39;s price in 3 different stores: store1, store2, and store3.
+If the product is not available in a store, the price will be null in that store&#39;s column.
+</pre>
+
+<p>&nbsp;</p>
+
+<p>Write an SQL query to rearrange the <code>Products</code> table so that each row has <code>(product_id, store, price)</code>. If a product is not available in a store, do <strong>not</strong> include a row with that <code>product_id</code> and <code>store</code> combination in the result table.</p>
+
+<p>Return the result table in <strong>any order</strong>.</p>
+
+<p>The query result format is in the following example.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> 
+Products table:
++------------+--------+--------+--------+
+| product_id | store1 | store2 | store3 |
++------------+--------+--------+--------+
+| 0          | 95     | 100    | 105    |
+| 1          | 70     | null   | 80     |
++------------+--------+--------+--------+
+<strong>Output:</strong> 
++------------+--------+-------+
+| product_id | store  | price |
++------------+--------+-------+
+| 0          | store1 | 95    |
+| 0          | store2 | 100   |
+| 0          | store3 | 105   |
+| 1          | store1 | 70    |
+| 1          | store3 | 80    |
++------------+--------+-------+
+<strong>Explanation:</strong> 
+Product 0 is available in all three stores with prices 95, 100, and 105 respectively.
+Product 1 is available in store1 with price 70 and store3 with price 80. The product is not available in store2.
+</pre>