Table schema:
CREATE TABLE station (city VARCHAR, id VARCHAR); CREATE TABLE trip (end_station_id VARCHAR, id VARCHAR); CREATE TABLE station (id VARCHAR, city VARCHAR); CREATE TABLE trip (start_station_id VARCHAR, id VARCHAR)

Question: How many trips started from Mountain View city and ended at Palo Alto city?
SQL: SELECT COUNT(*) FROM station AS T1 JOIN trip AS T2 JOIN station AS T3 JOIN trip AS T4 ON T1.id = T2.start_station_id AND T2.id = T4.id AND T3.id = T4.end_station_id WHERE T1.city = "Mountain View" AND T3.city = "Palo Alto"