You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'AND id_product = 0), st' at line 2

UPDATE ps_cart_product SET rental_days = 
												(SELECT rental_days FROM ps_products_in_availability_check WHERE id_customer =   AND id_product = 0), 																														
												
										   start_date = 
												(SELECT start_date FROM ps_products_in_availability_check WHERE id_customer =   AND id_product = 0),

											svdays = 
												(SELECT svdays FROM ps_products_in_availability_check WHERE id_customer =   AND id_product = 0),

											end_date = 
												(SELECT end_date FROM ps_products_in_availability_check WHERE id_customer =   AND id_product = 0)
						WHERE id_product = 0 AND start_date IS NULL