Use Access expression builder to calculate field data from another field

1. after the database file is opened, select 查詢設計

2. select the database table which will be used  in the query

3.  select the any data field to display for index in the final query table

4. keep the focus(cursor) on the new display field to input expression

5. press on the expression builder to help to construct the expression

6. input the expression to generate the new field data

7. select 執行(execution) to generate the query result

8. in the query result, you may mark the whole column, then copy/paste to overwrite the original database table

instead of using expression builder in step 6, it is more convenient to
copy/paste the existing expression directly to the field definition in step 7.

Expr1: IIf(InStr(1,[ktv_Song]![Song_FileName],"_gn")=0,40,Val(Mid([ktv_Song]![Song_FileName],InStr(1,[ktv_Song]![Song_FileName],"_gn")+3,2)))