Problem

Given a table with two columns, write a SQL query to find the most common value in the second column.
Example input:
id | value
1  | 3
2  | 5
3  | 3
4  | 3
5  | 5
Example output:
3

Solution

SELECT value, COUNT(*) AS count
FROM table
GROUP BY value
ORDER BY count DESC
LIMIT 1;

/*

The solution above is optimal because it uses the GROUP BY and ORDER BY clauses to group the values and order them by count.
The LIMIT clause is used to limit the result to one row.

*/