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SQL practice question · Hard · Recursive & Hierarchy · Google

staff has one row per employee (employee_id, manager_id, title); manager_id references another employee and is NULL at the top. An employee counts as a manager when at least one employee reports to them (the title column is informational only and must not be used). Return every manager who has at least one direct report who is also a manager, together with the number of such direct reports. Output columns: manager_id, manager_reports. Order by manager_id ascending.

Table: staff

Schema of staff
Column	Type
employee_id	INTEGER
manager_id	INTEGER
title	TEXT

Schema of staff

Column

Type

employee_id

INTEGER

manager_id

INTEGER

title

TEXT

Sample rows of staff
employee_id	manager_id	title
1	NULL	Director
2	1	supervisor
3	2	Analyst
4	1	supervisor
5	4	Analyst
6	2	Analyst

Sample rows of staff

employee_id

manager_id

title

NULL

Director

supervisor

Analyst

supervisor

Analyst

Expected output on the sample data
manager_id	manager_reports
1	2

Expected output on the sample data

manager_id

manager_reports

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