> 1111 - Invalid use of group function

1111 - "Invalid use of group function" 这个错误通常出现在数据库查询语句中，当你试图对聚合函数（如SUM、COUNT、AVG等）的结果进行进一步的操作，而这些操作不应该应用到结果集上时。在SQL查询中，group by 子句用于将数据分组，而聚合函数是对每个组内的数据进行计算。如果你试图直接对分组后的结果再次使用聚合函数，或者在group by 之外的地方引用分组字段，就会导致这个错误。

例如，下面的SQL是无效的，因为试图在`SUM(salary)`之后再进行计数：

SELECT department_id, SUM(salary), COUNT(*) 
FROM employees;

正确的做法应该是分开两个查询，或者针对每个组分别操作：

SELECT department_id, SUM(salary) as total_salary, COUNT(*) as employee_count
FROM employees
GROUP BY department_id;

OR

WITH grouped_data AS (
    SELECT department_id, SUM(salary) as total_salary
    FROM employees
    GROUP BY department_id
)
SELECT department_id, total_salary, (SELECT COUNT(*) FROM grouped_data WHERE department_id = grouped.department_id) as employee_count
FROM grouped_data grouped;