About report

Hello to all

In my family banking management project, I continue by coding a report (via ReportSQL). To do this, I use code from Derek used in another of his projects.
I have two questions ;
1 - How should we code the use of a cacculated field (here cftbalance) in a report ?
2 - What is the use of adding AS “transactions.date” and others. at the end of each  ?
If I remove it, there is no impact in my error message.

Here is this piece of code in which I include a calculated field. This bug (apparently a problem with misplaced parenthesis):

SELECT

strftime('%d/%m/%y',transactions.tdate) AS "transactions.date",
transactions.tdesc AS "transactions.tdesc",
type.ttype AS "type.ttype",
imputations.Imputation AS "imputations.imputation",
transactions.tpaidout AS "transactions.tpaidout",
transactions.tpaidin AS "transactions.tpaidin",
total(t.tpaidin) - total(t.tpaidout) from transactions t, accounts a where (t.tdate <= transactions.tdate) and t.id_accounts = a.id and transactions.id_accounts = a.id)) AS " transactions.cftbalance"
   
from transactions

Left outer join type on transactions.id = type.id_transactions
Left outer join imputations On transactions.id = imputations.id_transactions

Thank you in advance for your responses.

J.B.