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leetcode/problem/customers-who-bought-all-products.html

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+<p>Table: <code>Customer</code></p>
+
+<pre>
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| customer_id | int     |
+| product_key | int     |
++-------------+---------+
+This table may contain duplicates rows. 
+<code>customer_id</code> is not NULL<code>.</code>
+product_key is a foreign key (reference column) to <code>Product</code> table.
+</pre>
+
+<p>&nbsp;</p>
+
+<p>Table: <code>Product</code></p>
+
+<pre>
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| product_key | int     |
++-------------+---------+
+product_key is the primary key (column with unique values) for this table.
+</pre>
+
+<p>&nbsp;</p>
+
+<p>Write a solution to report the customer ids from the <code>Customer</code> table that bought all the products in the <code>Product</code> table.</p>
+
+<p>Return the result table in <strong>any order</strong>.</p>
+
+<p>The&nbsp;result format is in the following example.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> 
+Customer table:
++-------------+-------------+
+| customer_id | product_key |
++-------------+-------------+
+| 1           | 5           |
+| 2           | 6           |
+| 3           | 5           |
+| 3           | 6           |
+| 1           | 6           |
++-------------+-------------+
+Product table:
++-------------+
+| product_key |
++-------------+
+| 5           |
+| 6           |
++-------------+
+<strong>Output:</strong> 
++-------------+
+| customer_id |
++-------------+
+| 1           |
+| 3           |
++-------------+
+<strong>Explanation:</strong> 
+The customers who bought all the products (5 and 6) are customers with IDs 1 and 3.
+</pre>