用MySQL中的两个表计数问题

Question

i want to get number of records from two tables having less than 3 pics.here is what i have tried but this is not working well

SELECT
    SUM(tot_rent) AS tot_rent
    FROM (
    SELECT
            COUNT(id) AS tot_rent
        FROM crm_rentals_images
        GROUP BY rentals_id
        HAVING COUNT(*) <3
    UNION
    SELECT
            COUNT(id) AS tot_rent
        FROM crm_sales_images
        GROUP BY rentals_id
        HAVING COUNT(*) <3
    ) s

what is missing?when i am comparing with real data,it do not show correct result

CREATE TABLE IF NOT EXISTS `crm_rentals_images` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`image` varchar(22) NOT NULL,
`rentals_id` int(22) DEFAULT NULL,
 PRIMARY KEY (`id`)
 ) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=11 ;

INSERT INTO `crm_rentals_images` (`id`, `image`, `rentals_id`) VALUES
(1, 'a.jpg', 1),
(2, 'b.jpg', 1),
(3, 'a.jpg', 1),
(4, 'b.jpg', 1),
 (5, 'a.jpg', 2),
(6, 'b.jpg', 2),
(7, 'a.jpg', 4),
(8, 'b.jpg', 4),
(9, 'a.jpg', 3),
(10, 'b.jpg', 3);

Answer 1

Try your query like this

select
  count(id) as tot_rent
from (
    select
        count(id) as tot_rent
    from crm_rentals_images
    GROUP BY rentals_id
    HAVING tot_rent < 3 
    union ALL
    select
        count(id) as tot_rent
    from crm_sales_images
    GROUP BY rentals_id
    HAVING tot_rent < 3
    ) s
group by tot_rent