619. Biggest Single Number


Table number contains many numbers in column num including duplicated ones.
Can you write a SQL query to find the biggest number, which only appears once.

+---+
|num|
+---+
| 8 |
| 8 |
| 3 |
| 3 |
| 1 |
| 4 |
| 5 |
| 6 |
For the sample data above, your query should return the following result: 
+---+
|num|
+---+
| 6 |
Note:
If there is no such number, just output null.


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Solution

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Approach: Using subquery and MAX() function [Accepted]

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Algorithm

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Use subquery to select all the numbers appearing just one time.

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Then choose the biggest one using MAX().\n

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