MySQL - 加入的特定列？
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MySQL - specific columns on join?
提问by Mathias Lykkegaard Lorenzen
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?
在进行连接（内部、左外部、右外部或其他）时，如何指定表中的哪些列要加入原始表？
Consider the following example:
考虑以下示例：
SELECT FirstName FROM User LEFT OUTER JOIN Provider ON User.ProviderID = Provider.ID
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?
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 Provider 的哪些部分应包含在结果集中？
回答by Tudor Constantin
This will only include User.FirstNameand Provider.ProviderIDin the final resultset:
这将只包括User.FirstName并Provider.ProviderID在最终结果集中：
SELECT User.FirstName, Provider.ProviderID FROM User LEFT OUTER JOIN Provider ON User.ProviderID = Provider.ID
回答by Thomas
SELECT User.FirstName, Provider.ID, Provider.YourExtraColumnname, Provider.YourExtraColumnname2 FROM User LEFT OUTER JOIN Provider ON User.ProviderID = Provider.ID
回答by Shef
SELECT `User`.FirstName, Provider.*
FROM `User`
LEFT OUTER JOIN Provider
ON `User`.ProviderID = Provider.ID
1. You use the table name before the column, or if you alias your tables, you can use the alias.
1. 您在列之前使用表名，或者如果您为表设置别名，则可以使用别名。
E.g. LEFT OUTER JOIN Provider pand then you could access providers id on the select clause like this:
例如LEFT OUTER JOIN Provider p，然后您可以在 select 子句上访问提供者 ID，如下所示：
SELECT `User`.FirstName, p.ID
2. I added backticks around the table name User, because it is a reserved word for MySQL
2.我在表名周围加了反引号User，因为它是MySQL的保留字
回答by Shamim Hafiz
You can specify the specific items to choose, like:
您可以指定要选择的特定项目，例如：
SELECT User.FirstName, Provider.ID, Provider.Name FROM User LEFT OUTER JOIN Provider ON User.ProviderID = Provider.ID
