LeetCode MySQL-1965. Employees With Missing Information

    AllenLi
    LeetCode MySQL

    Write an SQL query to report the IDs of all the employees with missing information. The information of an employee is missing if:
    The employee’s name is missing, or
    The employee’s salary is missing.
    Return the result table ordered by employee_id in ascending order.

    寫一個 SQL Query來報告全部的 IDs 中有缺少資訊的員工編號。
依照employee_id來排序結果。

    Table: Employees

    +-------------+---------+
| Column Name | Type    |
+-------------+---------+
| employee_id | int     |
| name        | varchar |
+-------------+---------+
employee_id is the primary key for this table.
Each row of this table indicates the name of the employee whose ID is employee_id.

    Table: Salaries

    +-------------+---------+
| Column Name | Type    |
+-------------+---------+
| employee_id | int     |
| salary      | int     |
+-------------+---------+
employee_id is the primary key for this table.
Each row of this table indicates the salary of the employee whose ID is employee_id.

    Example 1:

    Input: 
Employees table:
+-------------+----------+
| employee_id | name     |
+-------------+----------+
| 2           | Crew     |
| 4           | Haven    |
| 5           | Kristian |
+-------------+----------+
Salaries table:
+-------------+--------+
| employee_id | salary |
+-------------+--------+
| 5           | 76071  |
| 1           | 22517  |
| 4           | 63539  |
+-------------+--------+
Output: 
+-------------+
| employee_id |
+-------------+
| 1           |
| 2           |
+-------------+
Explanation: 
Employees 1, 2, 4, and 5 are working at this company.
The name of employee 1 is missing.
The salary of employee 2 is missing.

    Solution:
    1. 確認來自 Employees 的 employee_id 且不存在 Salaries。
    2. 合併 Employees 與 Salaries 兩個 table。
    3. 確認來自 Salaries 的 employee_id 且不存在 Employees。
    4. 依照 employee_id 進行排序。

    Code.1:

    SELECT employee_id FROM Employees 
WHERE employee_id NOT IN(SELECT employee_id FROM Salaries)
UNION
SELECT employee_id FROM Salaries 
WHERE employee_id NOT IN(SELECT employee_id FROM Employees)
ORDER BY employee_id;

    newEmployees

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