mysql - 显示作为另一个表中主键的列的计数

Question

将 2 个表作为输入 - Employee 和 Contact 为:

Employee  
ID  Name  
1   Anshika   
2   Arnav   
3   Ishita  
4   Iti  

Contact  
ID  Mobile No.  
1   1234  
2   2345  
4   3456  
2   4532  
1   5674  

显示输出为:

ID      COUNT  
1       2  
2       2  
3       0  
4       1  

我写道:

SELECT id, COUNT(*) FROM Contact GROUP BY id;

输出为:

ID COUNT  
1 2  
2 2  
4 1  

但我希望输出中也有 3 0 记录。

Answer 1

这对你有用:**

SELECT nameemp.id, 
COUNT(Contact.ID) AS total
FROM nameemp 
LEFT JOIN Contact
ON nameemp.id = Contact.id
GROUP BY nameemp.id

**