Bill和Sascha的评论激励我提供一种可能的解决方案：

Bill's and Sascha's comments inspired me to provide one of possible solutions:

//LinqPad sample
DataTable dt1 = new DataTable();
DataColumn dc = new DataColumn("ID", Type.GetType("System.String"));
dt1.Columns.Add(dc);
for (int i=10; i<30; i++)
{
    dt1.Rows.Add(new Object[]{string.Concat("CHARG", i.ToString())});
}

DataTable dt2 = new DataTable();
dc = new DataColumn("ID", Type.GetType("System.String"));
dt2.Columns.Add(dc);
for (int i=10; i<30; i++)
{
    dt2.Rows.Add(new Object[]{string.Concat("charg", i.ToString())});
}

//cross join uses cartesian algorithm
var qry = from r1 in dt1.AsEnumerable()
    from r2 in dt2.AsEnumerable()
    let comp_res = String.Equals(r1.Field<string>("ID"), r2.Field<string>("ID"), StringComparison.OrdinalIgnoreCase)
    where comp_res
    select new
    {
        r1_ID = r1.Field<string>("ID"),
        r2_ID = r2.Field<string>("ID"),
        comp_result = comp_res
    };
//dump qry object
qry.Dump();

结果：

Result:

r1_ID    r2_ID  comp_result
CHARG10 charg10 True 
CHARG11 charg11 True 
CHARG12 charg12 True 
...
CHARG29 charg29 True 

注意：这只是一个示例，但它可以帮助您解决问题。

Note: it's just a sample, but it might help you to solve your issue.

做类似的事情

var user = UserTable.FirstOrDefault(u=>String.Equals(u.ID, targetString, StringComparison.OrdinalIgnoreCase));