Question

我有下表，每个员工都有一个经理，如果一个人是他自己的经理，那么managerid字段为空，我希望emid name and manager id因为结果表名是员工

emid name managerid
1    raj  null
2    ram   1
3    ravi   null
4    arvind  3
5    rithu   2

我希望结果为

emid name managername
1    raj  raj
2    ram   raj
3    ravi   ravi
4    arvind  ravi
5    rithu   ram

Answer 1

SELECT e1.emid, e1.name, COALESCE(e2.name, e1.name) AS managername
    FROM employee e1
        LEFT JOIN employee e2
            ON e1.managerid = e2.emid

Answer 2

UNTESTED：

select a.name as name, b.name as managername from employee a inner join employee b on a.managerid=b.emid

这只会让实际拥有经理的员工屈服。但这就是你加入桌子的方式。

Answer 3

select
      e1.emid,
      e1.name,
      COALESCE(e2.name, e1.name ) ManagerName
   from 
      employees e1
         left join employees e2
            on e1.managerid = e2.emid

Answer 4

SELECT emid, name,
       CASE WHEN s.managerid IS NULL THEN s.name ELSE m.name END managername
  FROM employees s
  LEFT JOIN employees m ON s.managerid = m.managerid

OR

SELECT emid, name, m.name managername
  FROM employees s
  LEFT JOIN employees m ON COALESCE(s.managerid, s.emid) = m.emid

在mysql中加入相同的表？

4 个答案: