add leetcode problem-cn part3

算法题（国内版）/problem (English)/超过5名学生的课(English) [classes-more-than-5-students].html

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+<p>Table: <code>Courses</code></p>
+
+<pre>
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| student     | varchar |
+| class       | varchar |
++-------------+---------+
+(student, class) is the primary key column for this table.
+Each row of this table indicates the name of a student and the class in which they are enrolled.
+</pre>
+
+<p>&nbsp;</p>
+
+<p>Write an SQL query to report all the classes that have <strong>at least five students</strong>.</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> 
+Courses table:
++---------+----------+
+| student | class    |
++---------+----------+
+| A       | Math     |
+| B       | English  |
+| C       | Math     |
+| D       | Biology  |
+| E       | Math     |
+| F       | Computer |
+| G       | Math     |
+| H       | Math     |
+| I       | Math     |
++---------+----------+
+<strong>Output:</strong> 
++---------+
+| class   |
++---------+
+| Math    |
++---------+
+<strong>Explanation:</strong> 
+- Math has 6 students, so we include it.
+- English has 1 student, so we do not include it.
+- Biology has 1 student, so we do not include it.
+- Computer has 1 student, so we do not include it.
+</pre>