CREATE TABLE employees (department_id VARCHAR, employee_id VARCHAR)
CREATE TABLE departments (department_id VARCHAR, manager_id VARCHAR)

get the details of employees who manage a department.
SELECT DISTINCT * FROM employees AS T1 JOIN departments AS T2 ON T1.department_id = T2.department_id WHERE T1.employee_id = T2.manager_id
SELECT DISTINCT * FROM "employees" AS "T1" JOIN "departments" AS "T2" ON "T1"."department_id" = "T2"."department_id" AND "T1"."employee_id" = "T2"."manager_id"