Question

我正在尝试使用INNER JOIN函数从多个表中提取特定信息，并且我认为我的语法有问题-想到太多或太少（）。社区对此有何看法？

SELECT Employee.EmployeeID
    ,Service.HoursWorked
FROM (
    Equipment INNER JOIN (Equipment Repair)
        ON Equipment.EquipmentID = Equipment Repair.RepairID
    )
INNER JOIN (
    (
        (
            Service INNER JOIN EMPLOYEE
                ON Service.ProductID = EMPLOYEE.EmployeeID
            ) INNER JOIN (
            OWNER INNER JOIN Property
                ON OWNER.OwnerID = Property.OwnerID
            )
        INNER JOIN SubProperty
            ON Property.PropertyID = SubProperty.PropertyID
        )
    ON Service.PropertyID = Subproperty.PropertyID
    )
INNER JOIN TrainingCourse
    ON EMPLOYEE.EmployeeID = TrainingCourse.EmployeeID
        ON Equipment.EquipmentID = TrainingCourse.EquipmentID ORDER BY Employee.EmployeeID

Answer 1

您的查询正在尝试将多个表连接在一起，但是您可能也在尝试使用括号吗？这些没有您可能期望的效果。

没有（显然吗？）假括号，我将理解该查询的含义：

SELECT
    Employee.EmployeeID
    ,Service.HoursWorked
FROM Equipment
    INNER JOIN (Equipment Repair)
        ON Equipment.EquipmentID = Equipment Repair.RepairID
    INNER JOIN Service
    INNER JOIN EMPLOYEE
        ON Service.ProductID = EMPLOYEE.EmployeeID
    INNER JOIN OWNER
    INNER JOIN Property
        ON OWNER.OwnerID = Property.OwnerID
    INNER JOIN SubProperty
        ON Property.PropertyID = SubProperty.PropertyID
        ON Service.PropertyID = Subproperty.PropertyID
    INNER JOIN TrainingCourse
        ON EMPLOYEE.EmployeeID = TrainingCourse.EmployeeID
        ON Equipment.EquipmentID = TrainingCourse.EquipmentID
ORDER BY Employee.EmployeeID

但这仍然存在错误，因为许多联接缺少联接条件，而有些联接具有多个联接条件。

相反，您需要考虑要表达的projection operation。结果集中应该出现哪些列，哪些表（告诉您要联接的表），以及在什么条件下表Foo中的行应出现在总结果集中（告诉您该表的联接条件）

我在此访问SQL查询中缺少什么？

1 个答案: