Query either field with highest number

I have 2 fields in a database table: "up" and "down" and they both have integer values.

up = 8
down = 4

To pull rows where up is more than down I use

$q开发者_运维知识库uery = "SELECT * FROM table WHERE up > down";

Suppose I want to pull the value of either field that has the highest number. How would I do this in a query?

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SELECT IF(a > b, a, b) AS max_value
  FROM (SELECT MAX(up) AS a,
               MAX(down) AS b
          FROM table) x

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I found that the greatest() function is ideal for my case http://dev.mysql.com/doc/refman/5.0/en/comparison-operators.html#function_greatest

SELECT GREATEST( up, down ) FROM table