MySQL - 特定的连接列？

Question

在进行连接(内部,左外部,右外部或其他)时,如何指定表中哪些列连接到原始表？

请考虑以下示例:

SELECT FirstName FROM User LEFT OUTER JOIN Provider ON User.ProviderID = Provider.ID

这将从用户中选择FirstName,但从Provider中选择所有内容.如何指定结果集中应包含Provider的哪些部分？

Answer 1

像这样:

SELECT User.FirstName, Provider.* FROM User LEFT OUTER JOIN Provider ON User.ProviderID = Provider.ID

Answer 2

  SELECT User.FirstName, Provider.ID, Provider.YourExtraColumnname, Provider.YourExtraColumnname2 FROM User LEFT OUTER JOIN Provider ON User.ProviderID = Provider.ID