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49 lines
1.6 KiB
HTML
49 lines
1.6 KiB
HTML
<p>Table: <code>Orders</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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| order_number | int |
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| customer_number | int |
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+-----------------+----------+
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order_number is the primary key for this table.
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This table contains information about the order ID and the customer ID.
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</pre>
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<p> </p>
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<p>Write an SQL query to find the <code>customer_number</code> for the customer who has placed <strong>the largest number of orders</strong>.</p>
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<p>The test cases are generated so that <strong>exactly one customer</strong> will have placed more orders than any other customer.</p>
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<p>The query result format is in the following example.</p>
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<p> </p>
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<p><strong>Example 1:</strong></p>
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<pre>
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<strong>Input:</strong>
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Orders table:
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+--------------+-----------------+
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| order_number | customer_number |
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+--------------+-----------------+
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| 1 | 1 |
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| 2 | 2 |
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| 3 | 3 |
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| 4 | 3 |
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+--------------+-----------------+
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<strong>Output:</strong>
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+-----------------+
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| customer_number |
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+-----------------+
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| 3 |
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+-----------------+
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<strong>Explanation:</strong>
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The customer with number 3 has two orders, which is greater than either customer 1 or 2 because each of them only has one order.
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So the result is customer_number 3.
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</pre>
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<p> </p>
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<p><strong>Follow up:</strong> What if more than one customer has the largest number of orders, can you find all the <code>customer_number</code> in this case?</p>
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