SQL查询拉同一个字段不同的值

Question

我有两张表，员工记录（id，firstName，lastName）和违规（violatorId，supervisorId）。

我的查询提取了违规者和主管的列表。我宁愿不显示该人的身份证，显示他们的名字和姓氏。所以这是我的查询到目前为止...

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，这将返回第一个和最后一个名称信息，违反者，而不是管理者。示例输出：

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

任何帮助将是巨大的

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

你需要参加一次以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

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 

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