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1965_employees_with_missing_information.md

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Employees With Missing Information

SQL Schema

Create table If Not Exists Employees (employee_id int, name varchar(30));
Create table If Not Exists Salaries (employee_id int, salary int);
Truncate table Employees;
insert into Employees (employee_id, name) values ('2', 'Crew');
insert into Employees (employee_id, name) values ('4', 'Haven');
insert into Employees (employee_id, name) values ('5', 'Kristian');
Truncate table Salaries;
insert into Salaries (employee_id, salary) values ('5', '76071');
insert into Salaries (employee_id, salary) values ('1', '22517');
insert into Salaries (employee_id, salary) values ('4', '63539');

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.

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.

The query result format is in the following example.

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

SELECT employee_id
FROM (
       SELECT employee_id employee_id  FROM Employees
       UNION ALL
       SELECT employee_id employee_id  FROM Salaries
) AS a
GROUP BY employee_id  
HAVING COUNT(*) = 1 
Order by employee_id ASC