Add: Biggest Single Number

Author: Openset

problems/biggest-single-number/README.md

@@ -1,2 +1,25 @@
 ## 619. Biggest Single Number
 
+<p>
+Table <code>number</code> contains many numbers in column <b>num</b> including duplicated ones.<br>
+Can you write a SQL query to find the biggest number, which only appears once.<br>
+</p>
+<pre>+---+
+|num|
++---+
+| 8 |
+| 8 |
+| 3 |
+| 3 |
+| 1 |
+| 4 |
+| 5 |
+| 6 | 
+</pre>
+For the sample data above, your query should return the following result:
+<pre>+---+
+|num|
++---+
+| 6 |
+</pre>
+<b>Note:</b><br> If there is no such number, just output <b>null</b>.<p></p>

problems/biggest-single-number/biggest_single_number.go

@@ -0,0 +1,17 @@
+# Write your MySQL query statement below
+
+# Method 1
+SELECT num
+FROM
+  `number`
+GROUP BY num
+HAVING COUNT(num) = 1;
+
+# Method 2
+SELECT MAX(num) AS num
+FROM
+  (SELECT num
+   FROM
+     number
+   GROUP BY num
+   HAVING COUNT(num) = 1) AS t;