MySQL regex update

Simple solution:

UPDATE  table
SET     words = REPLACE(words, 'brown', 'green')
WHERE   words REGEXP 'brown ' OR words REGEXP ' brown'

Better solution from http://techras.wordpress.com/2011/06/02/regex-replace-for-mysql/:

SET sql_mode='NO_BACKSLASH_ESCAPES';

DELIMITER $$
CREATE FUNCTION  `regex_replace`(pattern VARCHAR(1000),replacement VARCHAR(1000),original VARCHAR(1000))

RETURNS VARCHAR(1000)
DETERMINISTIC
BEGIN
 DECLARE temp VARCHAR(1000);
 DECLARE ch VARCHAR(1);
 DECLARE i INT;
 SET i = 1;
 SET temp = '';
 IF original REGEXP pattern THEN
  loop_label: LOOP
   IF i>CHAR_LENGTH(original) THEN
    LEAVE loop_label;
   END IF;
   SET ch = SUBSTRING(original,i,1);
   IF NOT ch REGEXP pattern THEN
    SET temp = CONCAT(temp,ch);
   ELSE
    SET temp = CONCAT(temp,replacement);
   END IF;
   SET i=i+1;
  END LOOP;
 ELSE
  SET temp = original;
 END IF;
 RETURN temp;
END$$
DELIMITER ;