CREATE TABLE Lessons (customer_id VARCHAR)
CREATE TABLE Customers (customer_id VARCHAR, first_name VARCHAR)

How many lesson does customer with first name Ray took?
SELECT COUNT(*) FROM Lessons AS T1 JOIN Customers AS T2 ON T1.customer_id = T2.customer_id WHERE T2.first_name = "Ray"
SELECT COUNT(*) FROM "Lessons" AS "T1" JOIN "Customers" AS "T2" ON "Ray" = "T2"."first_name" AND "T1"."customer_id" = "T2"."customer_id"