mysql show每行中其他表的行數

Question

select `personal`.`id` AS `id`, 
`personal`.`name` AS `name`, 
(select count(visit.id) 
     from visit,personal 
     where visit.user_id=personal.id) as count 
from personal; 

即時通訊嘗試獲取所有用戶和訪問次數。

我得到的結果是所有用戶，但count列包含相同的值（不是特定於該行ID）。

我在這裏做錯了什麼？如何告訴mysql用戶這行ID？

是複合選擇最佳的方式來做到這一點或有沒有更好的方法？

Answer 1

SELECT p.id, p.name, COUNT(v.user_id) 
FROM personal p 
LEFT JOIN 
     visit v 
ON  v.user_id = p.id 
GROUP BY 
     p.id 

您也可以使用過程中的子查詢（例如，如果您有ANSIGROUP BY兼容性）：

SELECT p.id, p.name, 
     (
     SELECT COUNT(*) 
     FROM visit v 
     WHERE v.user_id = p.id 
     ) 
FROM personal p 

Answer 2

試試這個

SELECT 
Pe.id AS id,Pe.name AS name,COUNT(v.user_id) number_visit 
FROM personal Pe 
LEFT JOIN visit Vi 
    ON Vi.user_id= Pe.id 
GROUP BY Pe.id 

Answer 3

將與LEFT JOIN表personal一起工作visit。

SELECT 
    Pe.id AS id, Pe.name AS name, COUNT(v.user_id) number_visit 
FROM 
    personal Pe 
LEFT JOIN 
    visit Vi ON Vi.user_id = Pe.id 
GROUP BY Pe.id 

如果你想只有那些有ATLEAST訪問數1用戶，請RIGHT JOIN或HAVING在Group By

SELECT 
    Pe.id AS id, Pe.name AS name, COUNT(v.user_id) number_visit 
FROM 
    personal Pe 
RIGHT JOIN 
    visit Vi ON Vi.user_id = Pe.id 
GROUP BY Pe.id 

OR

SELECT 
    Pe.id AS id, Pe.name AS name, COUNT(v.user_id) number_visit 
FROM 
    personal Pe 
LEFT JOIN 
    visit Vi ON Vi.user_id = Pe.id 
GROUP BY Pe.id HAVING number_visit > 1 

Answer 4

試試這個：

select 
    p.id AS `id`, 
    p.name AS `name`, 
    IFNULL(v.TheCount, 0) TheCount 
from personal p 
LEFT JOIN 
( 
    SELECT user_id, COUNT(*) TheCount 
    FROM visits v 
    GROUP BY user_id 
) v ON v.user_id = p.Id;