Compare values of two columns then select the larger value

Question

I need to query a table and select 3 of the values of 4 columns. I need to compare the values of the 3rd column and the fourth column and select the larger value.

For ex

Answer 1

I would start by creating a view.

CREATE VIEW t_c
SELECT id, c1 AS c FROM t
UNION
SELECT id, c2 AS c FROM t;

Then I would select from that view.

SELECT id, MAX(c) FROM t_c GROUP BY id;