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51 lines
1.6 KiB
HTML
51 lines
1.6 KiB
HTML
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<p>表：<code>Products</code></p>
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<pre>
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+-------------+---------+
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| Column Name | Type |
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+-------------+---------+
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| product_id | int |
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| store1 | int |
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| store2 | int |
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| store3 | int |
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+-------------+---------+
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这张表的主键是product_id（产品Id）。
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每行存储了这一产品在不同商店store1, store2, store3的价格。
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如果这一产品在商店里没有出售，则值将为null。
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</pre>
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<p> </p>
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<p>请你重构 <code>Products</code> 表，查询每个产品在不同商店的价格，使得输出的格式变为<code>(product_id, store, price)</code> 。如果这一产品在商店里没有出售，则不输出这一行。</p>
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<p>输出结果表中的 <strong>顺序不作要求</strong> 。</p>
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<p>查询输出格式请参考下面示例。</p>
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<p> </p>
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<p><strong>示例 1：</strong></p>
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<pre>
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<strong>输入：</strong>
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Products table:
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+------------+--------+--------+--------+
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| product_id | store1 | store2 | store3 |
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+------------+--------+--------+--------+
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| 0 | 95 | 100 | 105 |
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| 1 | 70 | null | 80 |
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+------------+--------+--------+--------+
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<strong>输出：</strong>
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+------------+--------+-------+
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| product_id | store | price |
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+------------+--------+-------+
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| 0 | store1 | 95 |
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| 0 | store2 | 100 |
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| 0 | store3 | 105 |
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| 1 | store1 | 70 |
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| 1 | store3 | 80 |
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+------------+--------+-------+
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<strong>解释：</strong>
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产品0在store1，store2,store3的价格分别为95,100,105。
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产品1在store1，store3的价格分别为70,80。在store2无法买到。</pre>
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