[GENERAL] two field table: field1, field2, how to add a third one with the auto-generated value replace(field2,'channel','AAAA')?

[zxo102 ouyang]

Hi evreyone,
   I have a table with two fields

   field1    field2
    1         1channel
    2         2channel
    3         3channel

Now I want to add the third one with the value
replace(field2,'channel','AAAA') like

    field1    field2           field3
    1         1channel    replace(field2,'channel','AAAA')
    2         2channel    replace(field2,'channel','AAAA')
    3         3channel    replace(field2,'channel','AAAA')

The field3 must be done automatically after a user input data into field1
and field2.

Any ideas?   Thanks a lot.

ouyang