MySQL-关于联接的特定列? [英] MySQL - specific columns on join?

问题描述

进行联接时(内部，左外部，右外部或其他)，如何指定表中的哪些列联接到原始表中?

When making a join (inner, left outer, right outer or whatever), how can I specify which columns on the table to join into the original table?

请考虑以下示例:

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

这将从用户中选择名字，但从提供者中选择所有内容.如何指定结果集中应包含提供者的哪些部分?

This would select FirstName from user, but select everything from Provider. How can I specify which parts of Provider should be included in the resultset?

推荐答案

这将在最终结果集中仅包括User.FirstName 和Provider.ProviderID :

This will only include User.FirstName and Provider.ProviderID in the final resultset:

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

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