摘录自:http://topic.youkuaiyun.com/t/20020124/13/496194.html
update tabname set colname=replace(colname,substring(colname,3,2),'xx')
update table set colname=replace(colname,'aaa','bbb')
update YourTableName set ColName=stuff(colname,3,2,'YY') (未测试)