替换all spaces:

UPDATE `table` SET `col_name` = REPLACE(`col_name`, ' ', '')

要删除所有tabs个字符:

UPDATE `table` SET `col_name` = REPLACE(`col_name`, '\t', '' )

要删除所有new line个字符:

UPDATE `table` SET `col_name` = REPLACE(`col_name`, '\n', '')

http://dev.mysql.com/doc/refman/5.0/zh-CN/string-functions.html#function_replace

要删除列的first and last space(s):

UPDATE `table` SET `col_name` = TRIM(`col_name`)

http://dev.mysql.com/doc/refman/5.0/zh-CN/string-functions.html#function_trim