CREATE TABLE customers (id VARCHAR, first_name VARCHAR, last_name VARCHAR)
CREATE TABLE invoices (total INT, customer_id VARCHAR)

What is the total amount of money spent by Lucas Mancini?
SELECT SUM(T2.total) FROM customers AS T1 JOIN invoices AS T2 ON T1.id = T2.customer_id WHERE T1.first_name = "Lucas" AND T1.last_name = "Mancini"
SELECT SUM("T2"."total") FROM "customers" AS "T1" JOIN "invoices" AS "T2" ON "T1"."id" = "T2"."customer_id" WHERE "Lucas" = "T1"."first_name" AND "Mancini" = "T1"."last_name"