您提供的示例数据和输出未演示左连接。如果是左联接，您的输出将如下所示（注意，我们如何为用户1获得3个结果，即对于用户1的每个Growth记录一次）

User | age| Data |Growth
------------------------                           
1    |2   |43.5  |46.5                           
1    |2   |43.5  |49.5     
1    |2   |43.5  |48.5     
2    |3   |44.5  |                          
3    |4   |45.6  |

假设您仍然需要左联接；这是您在Linq中进行左联接的方法：

var results = from data in userData
              join growth in userGrowth
              on data.User equals growth.User into joined
              from j in joined.DefaultIfEmpty()
              select new 
              {
                  UserData = data,
                  UserGrowth = j
              };

如果要进行右连接，只需交换从中选择的表，如下所示：

var results = from growth in userGrowth
              join data in userData
              on growth.User equals data.User into joined
              from j in joined.DefaultIfEmpty()
              select new 
              {
                  UserData = j,
                  UserGrowth = growth
              };

该代码的重要部分是in语句，后跟DefaultIfEmpty。这告诉Linq如果另一个表中没有匹配的结果，我们希望具有默认值（即null）。