Problem

Given a table with two columns, write a SQL query to find the most common value in each column.
Input:
id | col1 | col2
1  | 3    | 2
2  | 3    | 2
3  | 3    | 1
4  | 1    | 2
5  | 2    | 1
Output:
col1 | col2
3    | 2

Solution

SELECT col1, col2
FROM table
GROUP BY col1, col2
ORDER BY COUNT(*) DESC
LIMIT 1;

/*

The above solution is optimal because it uses the GROUP BY and ORDER BY clauses to group the rows by the values in each column and then order them by the number of times each value appears in the table. The LIMIT clause is then used to return only the first row, which is the row with the most common value in each column.

*/