DataTable1的sql:

select distinct  a.*,t.id as serverid,b.id as deptid,....

DataTable2的sql:

select distinct a.*,0 as serverid, 32 as deptid,...

在调用dt1.Merge(dt2)的时候，由于两个serverid字段类型不一致，一个int32,一个int64，导致无法Merge。

用importRow的方式就可以合并了：

private DataTable MergeTable(DataTable dest, DataTable source)
        {
            DataRow[] sourceRows = source.Select();
            for (int i = 0; i < sourceRows.Length; i++)
            {
                dest.ImportRow(sourceRows[i]);
            }
            return dest;
        }