Update table based on another table in SQLite DataBase

I am using SQLite. There are two tables shown below.

Transaction_Tbl
ID    Name    Credit/Debit    Value
1     ABC        credit        10
1     ABC        credit        10
2     DEF        credit        20
2     DEF        debit         40

(record for third employee EFG not present in the table)

Based on the table, Average_Tbl must be updated as below...

Average_Table
ID    Name    Avg(Credit-Debit)
1     ABC     20
2     DEF     -20
3     EFG     0 (as no records for EFG in Transaction_Tbl)

Now if there is a record for EFG in Transaction_Tbl for Debit, then in Average_Tbl, the record for EFG must be negative (credit - debit => where credit must be taken as zero as no records for credit.).

How to do it?