顯示部門與上層部門 中文名稱 (SQL 查詢 虛擬表 + LEFT JOIN)(同一資料表變成兩份資料使用JOIN整合查詢)

虛擬表 : 

 (SELECT id,name FROM department) AS above

完整語法 : 

SELECT dep.name AS department_name,above.name AS above_department_name FROM department AS dep LEFT JOIN (SELECT id,name FROM department) AS above ON dep.unit=above.id