Datarow in datatable cannot be copied to another datatable.

Public static datatable initdgvprocessworker () {arraylist list = new arraylist (); datatable dt = new datatable (); string STR = "select workerno as employee ID, [name] as name, dutycontent as responsibilities, [Group]
As group name, upperson as upper layer "+" from userinfo where [group] = 'production worker '"; string sqlstr = dbhelper. dbhelpersql. dataquery (STR ). tables [0]; dt = dbhelper. dbhelpersql. dataquery (sqlstr ). tables [0]; datatable resulttable = DT. copy (); resulttable. clear (); For (INT I = 0; I <DT. rows. count; I ++) {string upperson = DT. rows [I] ["upper layer"]. tostring (); If (upperson. contains (this. name) {resulttable. importrow (DT. rows [I]); // put} resulttable. columns. remove ("upper layer"); Return resulttable ;}