按部门统计人数和工资总额，没有部门的员工也要作为一组输出。
dept_id 分组。dept_id 为 null 的员工（合同工）单独成一组，输出时这一组的 dept_id 为 null。headcount：组内员工人数。total_salary：组内工资之和（本题数据里工资不为 null）。输入
employees(emp_id, name, dept_id, manager_id, hire_date, salary, title, email)输出
列为 dept_id, headcount, total_salary，行顺序不限。
employees hr/employees
| # | emp_idint64 | namestring | dept_idint64 | manager_idint64 | hire_datedate | salaryint64 | titlestring | emailstring |
|---|---|---|---|---|---|---|---|---|
| 1 | 1 | Grace Liu | 1 | null | 2015-10-01 | 98000 | CEO | grace.liu@corp.example |
| 2 | 2 | Leo Wang | 2 | 1 | 2017-09-09 | 72000 | VP Engineering | leo.wang@corp.example |
| 3 | 3 | Sara Chen | 3 | 1 | 2020-06-05 | 70000 | VP Sales | sara.chen@corp.example |
| 4 | 4 | Lucas Zhang | 4 | 2 | 2023-04-20 | 52000 | Engineering Manager | lucas.zhang@corp.example |
| 5 | 5 | Mia Zhao | 5 | 2 | 2016-07-16 | 52000 | Data Manager | mia.zhao@corp.example |
| 6 | 6 | Kevin Wu | 3 | 3 | 2016-10-23 | 45000 | Sales Manager | kevin.wu@corp.example |
| 7 | 7 | Lily Xu | 6 | 4 | 2025-03-17 | 48000 | Infra Lead | lily.xu@corp.example |
| 8 | 8 | Tom Huang | 4 | 4 | 2022-01-03 | 46000 | Senior Engineer | tom.huang@corp.example |
| 9 | 9 | Liam Zhou | 4 | 4 | 2020-10-01 | 39000 | Software Engineer | liam.zhou@corp.example |
| 10 | 10 | Nina Yang | 4 | 4 | 2020-10-02 | 39000 | Software Engineer | nina.yang@corp.example |
| 11 | 11 | Oscar Lin | 4 | 8 | 2022-07-15 | 26000 | Junior Engineer | oscar.lin@corp.example |
| 12 | 12 | Linda Ma | 5 | 5 | 2016-08-25 | 41000 | Data Engineer | linda.ma@corp.example |
| 13 | 13 | Eric Sun | 5 | 5 | 2021-09-09 | 33000 | Data Analyst | eric.sun@corp.example |
| 14 | 14 | Ivy He | 5 | 5 | 2018-05-29 | 41000 | Data Engineer | ivy.he@corp.example |
| 15 | 15 | Lei Gao | 5 | 12 | 2016-06-02 | 27000 | Junior Data Engineer | lei.gao@corp.example |
| 16 | 16 | Hao Guo | 6 | 7 | 2016-12-18 | 44000 | Site Reliability Engineer | hao.guo@corp.example |
| 17 | 17 | Fang Luo | 6 | 7 | 2020-11-11 | 38000 | Infra engineer | fang.luo@corp.example |
| 18 | 18 | Jun Liang | 6 | 16 | 2020-09-08 | 25000 | Junior Engineer | jun.liang@corp.example |
| 19 | 19 | Dana Song | 3 | 6 | 2016-10-13 | 31000 | Account Executive | dana.song@corp.example |
| 20 | 20 | Victor Tang | 3 | 6 | 2018-09-12 | 31000 | Account Executive | victor.tang@corp.example |
| # | dept_idInt64 | headcountInt64 | total_salaryDecimal(precision=38, scale=0) |
|---|---|---|---|
| 1 | 2 | 2 | 138000.0 |
| 2 | 5 | 8 | 290000.0 |
| 3 | null | 2 | 46000.0 |
| 4 | 1 | 1 | 98000.0 |
| 5 | 3 | 10 | 357000.0 |
| 6 | 4 | 10 | 405000.0 |
| 7 | 6 | 6 | 218000.0 |
| 8 | 7 | 1 | 61000.0 |