Here is a SQL query that will find the total number of customers who have made transactions totaling over $1000:

```
SELECT COUNT(DISTINCT CustomerID) FROM transactions
WHERE CustomerID IN (
    SELECT CustomerID FROM transactions
    GROUP BY CustomerID
    HAVING SUM(TransactionAmount) > 1000
);
```

Explanation: The inner query finds all the customers whose transaction amounts total over $1000 by grouping the transactions by customer ID and using the `SUM` function to add up the total transaction amount for each customer. The outer query counts the number of unique customers whose IDs appear in the results of the inner query.
Data una tabella delle transazioni dei clienti con le colonne CustomerID, TransactionID e TransactionAmount, scrivere una query SQL per trovare il numero totale di clienti che hanno effettuato transazioni per un totale superiore a $1000.