子查询不是标识主查询的列

SELECT department_name, employee_name, salary
FROM employees e
WHERE salary = (
    SELECT MAX(salary)
    FROM employees
    WHERE department_id = e.department_id
);

SELECT *
FROM employees
WHERE (position, department_id) = (
    SELECT position, department_id
    FROM employees
    WHERE employee_id = 123
);

SELECT e.employee_name, d.department_name
FROM (
    SELECT employee_id, department_id
    FROM employees
    WHERE hire_date > '2020-01-01'
) e
JOIN departments d ON e.department_id = d.department_id;

-- 错误示例
SELECT employee_name
FROM employees
WHERE department_id = (
    SELECT department_id
    FROM departments
    WHERE department_name = 'Sales'
);

-- 正确示例
SELECT employee_name
FROM employees
WHERE department_id = (
    SELECT department_id
    FROM departments
    WHERE department_name = 'Sales'
    LIMIT 1
);