mysql 指定字段分组

-- 错误示例
SELECT department, name, AVG(salary) FROM employees GROUP BY department;

-- 正确示例
SELECT department, AVG(salary) FROM employees GROUP BY department;

SELECT department, AVG(salary) AS avg_salary FROM employees GROUP BY department ORDER BY avg_salary DESC;

SELECT COALESCE(department, 'Unknown') AS department, AVG(salary) FROM employees GROUP BY department;

-- 单字段分组示例
SELECT department, AVG(salary) AS avg_salary
FROM employees
GROUP BY department;

-- 多字段分组示例
SELECT department, job_title, AVG(salary) AS avg_salary
FROM employees
GROUP BY department, job_title;

-- 排序示例
SELECT department, AVG(salary) AS avg_salary
FROM employees
GROUP BY department
ORDER BY avg_salary DESC;

-- 处理空值示例
SELECT COALESCE(department, 'Unknown') AS department, AVG(salary) AS avg_salary
FROM employees
GROUP BY department;