SQL Exercise: Physicians who is the head of each department
SQL hospital Database: Exercise-3 with Solution
3. From the following tables, write a SQL query to identify the physicians who are the department heads. Return Department name as “Department” and Physician name as “Physician”.
Sample table: physician
Sample table: department
SELECT d.name AS "Department", p.name AS "Physician" FROM department d, physician p WHERE d.head=p.employeeid;
Department | Physician ------------------+-------------- General Medicine | Percival Cox Surgery | John Wen Psychiatry | Molly Clock (3 rows)
The said query in SQL that selects the "name" column alias as "Department" from the 'department' table and the "name" column alias as "physician" from the 'physician' table, but only for those physicians who are the head of their respective department.
This query uses an implicit join to combine the 'department' and 'physician' tables.
The "WHERE" clause specifies the condition that the "employeeid" of a physician should match the "head" column of their respective department .
E R Diagram of Hospital Database:
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Previous SQL Exercise: Find the nurse who are the head of their department.
Next SQL Exercise: Patients with at least one physician appointment.
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SQL: Tips of the Day
Grouped LIMIT in PostgreSQL: Show the first N rows for each group?
db=# SELECT * FROM xxx; id | section_id | name ----+------------+------ 1 | 1 | A 2 | 1 | B 3 | 1 | C 4 | 1 | D 5 | 2 | E 6 | 2 | F 7 | 3 | G 8 | 2 | H (8 rows)
I need the first 2 rows (ordered by name) for each section_id, i.e. a result similar to:
id | section_id | name ----+------------+------ 1 | 1 | A 2 | 1 | B 5 | 2 | E 6 | 2 | F 7 | 3 | G (5 rows)
PostgreSQL v9.3 you can do a lateral join
select distinct t_outer.section_id, t_top.id, t_top.name from t t_outer join lateral ( select * from t t_inner where t_inner.section_id = t_outer.section_id order by t_inner.name limit 2 ) t_top on true order by t_outer.section_id;
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