从SQL查询中的另一个表中添加计数

Question

我已经创建了一个使用连接的mysql查询在其中我得到了彼此进行聊天的朋友列表。该查询包含三个表。现在想要添加来自包含用户聊天的第4表的计数。我在该表中有一个列名readstatus，我在该表中检查消息是否被读取。现在我想补充一点，表的计数在此查询，但我没有得到正确的方法添加此这里是查询

SELECT c.c_id, u.first_name, u.last_name, u.user_name, u.online_status, c.user_one, c.user_two, u.user_img, c.property_id, p.locality, p.city 
FROM cpo_conversation c, 
     property_register u, 
     property_for_sale p 
WHERE CASE WHEN c.user_one = '19' THEN c.user_two = u.id 
      WHEN c.user_two = '19' THEN c.user_one = u.id END 
     (c.user_one = '19' OR c.user_two = '19') AND p.id = c.property_id 
ORDER BY c.c_id DESC 

Answer 1

SELECT (SELECT COUNT(*) from ***4th_table*** WHERE ***user_condition*** AND readstatus=1) as your_count, c.c_id, u.first_name, u.last_name, 
u.user_name, u.online_status, c.user_one, c.user_two, u.user_img, 
c.property_id, p.locality, p.city FROM cpo_conversation c, property_register 
u, property_for_sale p WHERE CASE WHEN c.user_one = '19' THEN c.user_two = 
u.id WHEN c.user_two = '19' THEN c.user_one = u.id END (c.user_one = '19' OR 
c.user_two = '19') AND p.id = c.property_id ORDER BY c.c_id DESC