Question

我有三张桌子。员工，项目（多对多）和员工项目。

我想检索每个员工的姓名及其各自的项目。

我试图使用此查询：

SELECT Employee.name, Project.name 
FROM Employee, Project
INNER JOIN EmployeeProject ON Employee.empNo = EmployeeProject.empNo
INNER JOIN EmployeeProject ON Project.projectNo = EmployeeProject.projectNo;

Access给了我一个语法错误。然后我尝试了这个查询并且它有效：

SELECT Employee.name, Project.name 
FROM Employee, Project, EmployeeProject
WHERE Employee.empNo = EmployeeProject.empNo AND EmployeeProject.projectNo = Project.projectNo;

我的问题是;可以使用WHERE来链接表，或者有更好的方法来实现它，比如INNER ......

此致

Answer 1

使用显式JOIN时，不会在FROM子句中使用逗号分隔表。显式JOIN的正确语法（优先于使用WHERE子句的旧隐式语法）是：

SELECT
  /* Probably will need to give these aliases since the're both called name */
  Employee.name AS empname,
  Project.name AS projname 
FROM 
  Employee
  /* Employee joins through EmployeeProject */
  INNER JOIN EmployeeProject ON Employee.empNo = EmployeeProject.empNo
  /* ...into Project */
  INNER JOIN Project ON Project.projectNo = EmployeeProject.projectNo;

如果Access抱怨，可能需要围绕join子句()（虽然我找不到指定它的文档）

FROM 
  (Employee
  INNER JOIN EmployeeProject ON Employee.empNo = EmployeeProject.empNo)
  INNER JOIN Project ON Project.projectNo = EmployeeProject.projectNo;

Answer 2

当您涉及的表格超过2个时，即使在Access 2010中，也需要 ARE 。
JOIN中表格的顺序是重要。你无法从员工跳转 - ＆gt;项目（无关）到EmployeeProject（加入两者）

这可行

SELECT Employee.name, Project.name 
FROM ((Employee
INNER JOIN EmployeeProject ON Employee.empNo = EmployeeProject.empNo)
INNER JOIN Project ON EmployeeProject.projectNo = Project.projectNo);

注意：您可以将外部括号放在FROM和最终;之间，但更安全的做法是始终包含它。

你可以嵌套连接 - 如果你像这样嵌套它们，保留表的顺序（Employee，Project，EmployeeProject）：

SELECT Employee.name, Project.name 
FROM Employee
INNER JOIN (Project 
            INNER JOIN EmployeeProject 
              ON EmployeeProject.projectNo = Project.projectNo)
  ON Employee.empNo = EmployeeProject.empNo;

LEFT

SELECT Employee.name, Project.name 
FROM ((Employee
LEFT JOIN EmployeeProject ON Employee.empNo = EmployeeProject.empNo)
LEFT JOIN Project ON EmployeeProject.projectNo = Project.projectNo);

注意：在数据表视图和表单中，生成的列名为“Employee.name”和“Project.name”，因此您不必显式别名，尽管它可能有用。

我可以使用INNER JOIN替换WHERE吗？

2 个答案:

这可行