MySQL - 归还所有没有预订的人？

Question

我正在努力让MySQL给我所有在某个时间没有预订的教练。此查询本质上是搜索查询。因此，请回复所有尚未预订的教师及其详细信息。有人可以帮我完成它。这让我疯了。

SELECT
  AddressTypes.AddressTypeName,
  Addresses.*,
  InstructorSettings.*,
  Users.*,
  BookedSlots.DateTime
FROM Users
  LEFT OUTER JOIN InstructorSettings
    ON Users.UserID = InstructorSettings.UserID
  LEFT OUTER JOIN Addresses
    ON Users.UserID = Addresses.UserID
  INNER JOIN AddressTypes
    ON Addresses.AddressTypeID = AddressTypes.AddressTypeID
  LEFT OUTER JOIN BookedSlots
    ON Users.UserID = BookedSlots.UserID
WHERE Users.AccountTYpe = 3 AND Addresses.PostCode1 IN ('l13') AND BookedSlots.DateTime <> '2013-04-25 11:00:00'

上面的查询不会返回任何内容，但如果我取出“AND BookedSlots.DateTime＆lt;＆gt;'2013-04-25 11:00:00'”，它会返回所有教师详细信息。

数据库

非常感谢任何帮助。

Answer 1

在我看来，您所寻找的是指定时间内BookedSlots中缺少记录。

我不确定这是否被视为MySQL最佳做法，但我通常不是使用join来完成该任务，而是使用子选择或临时表，如下所示：

SELECT
  AddressTypes.AddressTypeName,
  Addresses.*,
  InstructorSettings.*,
  Users.*,
FROM Users
  LEFT OUTER JOIN InstructorSettings
    ON Users.UserID = InstructorSettings.UserID
  LEFT OUTER JOIN Addresses
    ON Users.UserID = Addresses.UserID
  INNER JOIN AddressTypes
    ON Addresses.AddressTypeID = AddressTypes.AddressTypeID
WHERE Users.AccountType = 3 AND Addresses.PostCode1 IN ('l13') 
AND Users.UserID not in (SELECT BookedSlots.InstructorID FROM BookedSlots 
     WHERE BookedSlots.DateTime = '2013-04-25 11:00:00')

编辑：根据评论，更改select语句以废除BookedSlots，并选择子选项以返回InstructorId（在预订时与教师而不是学生匹配）。

Answer 2

要检查特定时间段上是否有任何预订，请在连接条件中包含时间段，并选择时间段ID为空的位置 - 如下所示：

SELECT
  AddressTypes.AddressTypeName,
  Addresses.*,
  InstructorSettings.*,
  Users.*,
  BookedSlots.DateTime
FROM Users
  LEFT OUTER JOIN InstructorSettings
    ON Users.UserID = InstructorSettings.UserID
  LEFT OUTER JOIN Addresses
    ON Users.UserID = Addresses.UserID
  INNER JOIN AddressTypes
    ON Addresses.AddressTypeID = AddressTypes.AddressTypeID
  LEFT OUTER JOIN BookedSlots
    ON Users.UserID = BookedSlots.UserID AND 
                      BookedSlots.DateTime = '2013-04-25 11:00:00'
WHERE Users.AccountTYpe = 3 AND 
      Addresses.PostCode1 IN ('l13') AND 
      BookedSlots.UserID is null