问题遇到的现象和发生背景
- 查询平均工资最低的部门信息
用代码块功能插入代码,请勿
SELECT *
FROM departments
WHERE department_id=(
SELECT department_id
FROM employees
GROUP BY department_id
HAVING AVG(salary)=(
SELECT AVG(salary)
FROM employees
GROUP BY department_id
ORDER BY AVG(salary)
LIMIT 0,1
)
);
运行结果及报错内容
HAVING AVG(salary)=(
SELECT AVG(salary)
FROM employees
GROUP BY department_id
ORDER BY AVG(salary)
LIMIT 0,1
)
这些代码中 SELECT 语句中使用了聚合函数,没有起别名,ORDER BY 语句中又使用了聚合函数,这样写会影响执行效率吗?最好的格式是要在SELECT 语句中加上别名,ORDER BY 语句中用上SELECT中加的别名吗