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leetcode-cn/problem (English)/查找合法邮箱(English) [find-valid-emails].html

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+<p>Table: <code>Users</code></p>
+
+<pre>
++-----------------+---------+
+| Column Name     | Type    |
++-----------------+---------+
+| user_id         | int     |
+| email           | varchar |
++-----------------+---------+
+(user_id) is the unique key for this table.
+Each row contains a user&#39;s unique ID and email address.
+</pre>
+
+<p>Write a solution to find all the <strong>valid email addresses</strong>. A valid email address meets the following criteria:</p>
+
+<ul>
+	<li>It contains exactly one <code>@</code> symbol.</li>
+	<li>It ends with <code>.com</code>.</li>
+	<li>The part before the <code>@</code> symbol contains only <strong>alphanumeric</strong> characters and <strong>underscores</strong>.</li>
+	<li>The part after the <code>@</code> symbol and before <code>.com</code> contains a domain name <strong>that contains only letters</strong>.</li>
+</ul>
+
+<p>Return<em> the result table ordered by</em> <code>user_id</code> <em>in</em> <strong>ascending </strong><em>order</em>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example:</strong></p>
+
+<div class="example-block">
+<p><strong>Input:</strong></p>
+
+<p>Users table:</p>
+
+<pre class="example-io">
++---------+---------------------+
+| user_id | email               |
++---------+---------------------+
+| 1       | alice@example.com   |
+| 2       | bob_at_example.com  |
+| 3       | charlie@example.net |
+| 4       | david@domain.com    |
+| 5       | eve@invalid         |
++---------+---------------------+
+</pre>
+
+<p><strong>Output:</strong></p>
+
+<pre class="example-io">
++---------+-------------------+
+| user_id | email             |
++---------+-------------------+
+| 1       | alice@example.com |
+| 4       | david@domain.com  |
++---------+-------------------+
+</pre>
+
+<p><strong>Explanation:</strong></p>
+
+<ul>
+	<li><strong>alice@example.com</strong> is valid because it contains one <code>@</code>, alice&nbsp;is alphanumeric, and example.com&nbsp;starts with a letter and ends with .com.</li>
+	<li><strong>bob_at_example.com</strong> is invalid because it contains an underscore instead of an <code>@</code>.</li>
+	<li><strong>charlie@example.net</strong> is invalid because the domain does not end with <code>.com</code>.</li>
+	<li><strong>david@domain.com</strong> is valid because it meets all criteria.</li>
+	<li><strong>eve@invalid</strong> is invalid because the domain does not end with <code>.com</code>.</li>
+</ul>
+
+<p>Result table is ordered by user_id in ascending order.</p>
+</div>