如何使用pivot或类似的东西返回查询结果

Question

我需要编写一个select来生成以下内容：

   r_country | s_country |     s_name  |  r_name | msg    |   date
     ca        au            bill       bob      'hi'       2/12/2010

这是我的数据：

tableA

EmployeeName   |  EmployeeID  | country
bill              1                au
bob               2                ca


tableB

Sender       |  Reciever  |  Msg | date
bill               bob       'hi'   12/12/2010

之前我尝试过加入，但我认为这只会为我加入的用户返回数据

Answer 1

你需要加入两次。

SELECT
  receiver.country    AS r_country,
  sender.country      AS s_country,
  data.Sender         AS s_name,
  data.Receiver       AS r_name,
  data.msg            AS msg,
  data.date           AS date
FROM
  TableB              AS data
LEFT JOIN
  TableA              AS sender
    ON sender.EmployeeName = data.Sender
LEFT JOIN
  TableA              AS receiver
    ON receiver.EmployeeName = data.Receiver

但请注意，您的数据（事实）表不应包含NAME。您应该使用实体的UniqueID，一个独立于实体属性的字段（例如名称，地址等）