Question

我有两个表，员工记录（id，firstName，lastName）和违规（violatorId，supervisorId）。

我的查询会列出违规者和监督者名单。我想而不是显示该人的身份，显示他们的名字和姓氏。所以这是我到目前为止的询问......

SELECT 
emp.firstName as vFirstName,
emp.lastName as vLastname,
v.violatorId, 
v.supervisorId,
emp.firstName as sFirstName,
emp.lastName as sLastName
FROM employee emp
LEFT JOIN violator v
ON violatorId = emp.id

因此，这将返回违规者的姓名和姓氏信息，但不会返回主管。样本输出：

Violator vFirstName  vLastName   Supervisor sFirstName sLastName
1        Jon         Smith       20         Jon        Smith

任何帮助都会很棒

Answer 1

SELECT 
  e1.firstName AS violatorFirstName,
  e1.lastName AS violatorLastName,
  e2.firstName AS supervisorFirstName,
  e2.lastName AS supervisorLastName
FROM violator v
LEFT JOIN employee e1 ON v.violatorId = e1.id
LEFT JOIN employee e2 ON v. supervisorId = e2.id

Answer 2

您需要再次加入employee：

SELECT emp.firstName AS vFirstName, emp.lastName AS vLastName,
       v.violatorId AS vId, v.supervisorId AS sId,
       s.firstName AS sFirstName, s.lastName AS sLastName
FROM employee emp
LEFT JOIN violator v ON v.violatorId = emp.id
LEFT JOIN employee s ON v.supervisorId = s.id

Answer 3

<强>方法-1

SELECT 
  e1.violatorId AS violatorId ,
  e1.firstName AS violatorName,
  e2.supervisorId AS supervisorId ,
  e2.firstName AS supervisorName
FROM violator v
LEFT JOIN employee e1 ON v.violatorId = e1.id
LEFT JOIN employee e2 ON v. supervisorId = e2.id

<强>方法-2

SELECT 
    v.violatorId,
    emp.firstName AS violatorName, 
    v.supervisorId,
    (SELECT firstName FROM employee WHERE employee.id = v.supervisorId) AS supervisorName
FROM 
    employee emp
LEFT JOIN 
    violator v
ON 
    violatorId = emp.id

SQL Query使用不同的值拉取相同的字段

3 个答案: