list departments without worker? the latter one is the prefered style of me

Treasury
Corporate Tax
Control And Credit
Shareholder Services
Benefits
Manufacturing
Construction
Contracting
Operations
IT Support
NOC
IT Helpdesk
Government Sales
Retail Sales
Recruiting
Payroll

16 rows selected.

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select department_name from departments where not exists (
select * from employees where employees.department_id=departments.department_id)

Id	Operation	Name	Rows	Cost (%CPU)
0	.SELECT STATEMENT		17	3 (0)
1	..NESTED LOOPS ANTI		17	3 (0)
2	...TABLE ACCESS FULL	DEPARTMENTS	27	3 (0)
3	...INDEX RANGE SCAN	EMP_DEPARTMENT_IX	41	0 (0)

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select department_name from departments left join employees using (department_id) where email is null

Id	.Operation	Name	Rows	Cost (%CPU)
0	.SELECT.STATEMENT		106	6 (17)
1	..FILTER.
2	...MERGE.JOIN.OUTER		106	6 (17)
3	....TABLE.ACCESS.BY.INDEX.ROWID	DEPARTMENTS	27	2 (0)
4	.....INDEX.FULL.SCAN	DEPT_ID_PK	27	1 (0)
5	....SORT.JOIN		107	4 (25)
6	.....TABLE.ACCESS.FULL	EMPLOYEES	107	3 (0)