如果我有两个表job，employee。 我需要从工作中选择所有并为每个工作追加员 worker 数。
假设的结果
job table
+-------------+-------------+
| id | name |
+-------------+-------------+
| 1 | Teacher |
+-------------+-------------+
| 2 | Engineer |
+-------------+-------------+
| 3 | Programmer |
+-------------+-------------+
employee table
+-------------+-------------+-------------+
| id | name | job_id |
+-------------+-------------+-------------+
| 1 | employee N | 1 |
+-------------+-------------+-------------+
| 2 | employee N | 2 |
+-------------+-------------+-------------+
| 3 | employee N | 3 |
+-------------+-------------+-------------+
| 4 | employee N | 1 |
+-------------+-------------+-------------+
| 5 | employee N | 3 |
+-------------+-------------+-------------+
| 6 | employee N | 1 |
+-------------+-------------+-------------+
我需要从工作中选择所有并为每个工作追加员 worker 数。
假设的结果
Result table
+-------------+-------------+--------------+
| id | name |employee count|
+-------------+-------------+--------------+
| 1 | Teacher | 3 |
+-------------+-------------+--------------+
| 2 | Engineer | 1 |
+-------------+-------------+--------------+
| 3 | Programmer | 2 |
+-------------+-------------+--------------+
最佳答案
我喜欢使用左连接:)
SELECT job.id, job.name, count( * ) AS 'employee count'
FROM job
LEFT JOIN employee
ON job.id = employee.job_id
GROUP BY job.id
关于mysql从多个表中选择计数，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/23602771/