Database schema:

CREATE TABLE cars (
	id INTEGER NOT NULL -- example: ['2', '1'],
	train_id INTEGER DEFAULT NULL -- example: ['2', '1'],
	position INTEGER DEFAULT NULL -- example: ['2', '1'],
	shape TEXT DEFAULT NULL -- example: ['rectangle', 'bucket'],
	len TEXT DEFAULT NULL -- example: ['long', 'short'],
	sides TEXT DEFAULT NULL -- example: ['not_double', 'double'],
	roof TEXT DEFAULT NULL -- example: ['none', 'peaked'],
	wheels INTEGER DEFAULT NULL -- example: ['2', '3'],
	load_shape TEXT DEFAULT NULL -- example: ['hexagon', 'circle'],
	load_num INTEGER DEFAULT NULL -- example: ['1', '3'],
	PRIMARY KEY (id), 
	CONSTRAINT fk_cars_trains FOREIGN KEY(train_id) REFERENCES trains (id)
)


CREATE TABLE trains (
	id INTEGER NOT NULL -- example: ['2', '1'],
	direction TEXT DEFAULT NULL -- example: ['west', 'east'],
	PRIMARY KEY (id)
)

Question: Please list the IDs of all the trains that run in the east direction and have less than 4 cars.
Evidence: less than 4 cars refers to carsNum < 4

SQL:
SELECT T1.id FROM trains AS T1 INNER JOIN ( SELECT train_id, MAX(position) AS carsNum FROM cars GROUP BY train_id ) AS T2 ON T1.id = T2.train_id WHERE T1.direction = 'east' AND T2.carsNum < 4