==== Сметки со највисоко вкупно трошење во изминатата година
{{{#!sql
CREATE OR REPLACE FUNCTION get_top_accounts_last_year()
RETURNS TABLE (
    account_name TEXT,
    total_spent NUMERIC
)
LANGUAGE plpgsql
AS $$
BEGIN
    RETURN QUERY
    SELECT 
        ta.account_name, 
        COALESCE(SUM(tb.spent_amount), 0) AS total_spent
    FROM transaction_breakdown tb
    JOIN transaction t 
        ON tb.transaction_id = t.transaction_id
    JOIN transaction_account ta 
        ON tb.transaction_account_id = ta.transaction_account_id
    WHERE t.date >= NOW() - INTERVAL '1 YEAR'
    GROUP BY ta.account_name
    ORDER BY total_spent DESC
    LIMIT 10;
END;
$$;
}}}

==== Релациона алгебра
- TA(transaction_account_id, account_name)
- TB(transaction_id, transaction_account_id, spent_amount)
- T(transaction_id, date)

JOIN на табелите:
- J1 ← TA ⨝,,TA.transaction_account_id = TB.transaction_account_id,, TB
- J2 ← J1 ⨝,,TB.transaction_id = T.transaction_id,, T

Филтрирање по последна година:
- F ← σ,,date >= NOW() - INTERVAL '1 YEAR',, (J2)

Групирање и агрегација по сметка:
- G ← γ,,account_name; SUM(spent_amount) → total_spent,,(F)

Подредување по вкупно потрошено и лимитирање:
- R_final ← τ,,total_spent DESC LIMIT 10,,(G)