Delphi 2010 : UniDAC vs Indy-MultiThread safety handleing method - mysql

Question

I am doing develop Indy based application.
Server has several Indy TCP Server components.
So It works under multi-threads and handles mysql db.
I have faced one problem.
That is about the exceptions of MySQL DB in threads.
When serveral threads attack to same db table, then It says me like follows
UniQuery_Mgr: Duplicate field name 'id'
UniQuery_Mgr: Field 'grp_id' not found //of course grp_id field is really existed.
Assertion failure (C:\Program Files (x86)\unidac539src\Source\CRVio.pas, line 255)
Commands out of sync; You can't run this command now
ReceiveHeader: Net packets out of order: received[0], expected[1]
UniQuery_Mgr: Cannot perform this operation on a closed dataset
How to do I ? UniQuery_Mgr is TUniQuery component.
and my query handling code is normally like this
Code 1
sql := 'SELECT * FROM data_writed;';//for example
UniQuery_Mgr.SQL.Clear;
UniQuery_Mgr.SQL.Add(sql);
UniQuery_Mgr.ExecSQL;
Code 2
try
sql := 'SELECT * FROM gamegrp_mgr;';
UniQuery_Mgr.SQL.Clear;
UniQuery_Mgr.SQL.Add(sql);
UniQuery_Mgr.ExecSQL;
if UniQuery_Mgr.RecordCount > 0 then
begin
MAX_GAME_GROUP_COUNT := UniQuery_Mgr.RecordCount + 1;
UniQuery_Mgr.First;
i := 1;
while not UniQuery_Mgr.Eof do
begin
Game_Group_ID[i] := UniQuery_Mgr.FieldByName('grp_id').AsInteger;
Game_Game_ID[i] := UniQuery_Mgr.FieldByName('game_id').AsInteger;
UniQuery_Mgr.Next;
Inc(i);
end;
end;
except
on E : Exception do
begin
EGAMEMSG := Format('GAME group read error: <%s> # %s',[ E.ToString, DateTimeToStr(now)]);
Exit;
end;
end;
Code 3
try
sql := 'UPDATE data_writed SET write_gamegrp = ' + QuotedStr('0') + ';';
UniQuery_Mgr.SQL.Clear;
UniQuery_Mgr.SQL.Add(sql);
UniQuery_Mgr.ExecSQL;
except
on E : Exception do
begin
EGAMEMSG := Format('data updating error: <%s> # %s',[ E.ToString, DateTimeToStr(now)]);
Exit;
end;
end;
My handling DB components is bad ? Other thread-safe method is existed???