.net 重新设置sqlserver表的数据时出错

我想根据assignto column对列数据进行分组。但是否出现错误

我的问题是

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从tn group by Assignto中选择*您不能按*分组。返回值必须在分组中或是聚合

my sql table data is 

column names & their datatypes are

column name           Datatype

installation_id        int(primarykey,identity(1,1))
Assignto               varchar 
customer_address       "
customer_contactno     "
package_details        "

1    ISP    N.G.O Colony    9841612124  Extended for 6 mnths
2    FE K.K Nagar   9865015695  expired
55  ISP02   aa          1234567890      aa
56  ISP02   asdf            0987654321      expired
57  ISP01   asdf        8907654321      Extended for 6 mnths
58  FE01    asdf        6789054321      expired
59  ISP02   asdf            5432109999      expired
60  DTo1    asdf            9999999999      expired

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您希望得到什么结果？您希望查询中返回的其他列会发生什么情况？每一列必须在GROUP BY子句中指定，或包含在COUNT、SUM或MAX等聚合函数中

Select AssignTo, Count(*) From tn Group by assignto