>Would you please tell me how can i append a record into the middle of table. example, i have 10 records in table, then could i append a new record to the third row?

Use INSERT to add a new record at the record pointer, and you'll need esclusive use. But why? You shouldn't be worrying about natural record order in code. Just primary keys. This is from the Hacker's Guide:

"Don't confuse this INSERT command with the SQL INSERT command, which is very useful."

Get the hint that INSERT is a good idea?