select 语句中变量赋值问题

Question

mydate:tdatetime;
mydate:=datetime(i,'12:00:00')
query1.sql.add('select * from tablename where datdiff(day,FieldName,:mydate)';

Answer 1

const 
  s:= 'select * from %s where xxx=:thedate'
var
  thedate:tdatetime;  query1.close;
  thedate:=datetime(i,'12:00:00')
  query1.sql.add(Format(s,[tablename,thedate]);
  query1.open;

Answer 2

Var
   I: TDate;
   TableName: String;
Begin
     With Query1 Do
     Begin
          SQL.Clear;
          SQL.Add('Select * From '+TableName);
          SQL.Add('Where Start_Day = :Start_Day');
          ParamByName('Start_Day').AsDateTime := I;
          Open;
     End;
End;

Answer 3

Var
  I: TDate;
  TableName: String;
Begin
    With Query1 Do
    Begin
          SQL.Clear;
          SQL.Add('Select * From '+TableName);
          SQL.Add('Where Start_Day = :Start_Day');
          Prepared ;  //最好加上这一句
          ParamByName('Start_Day').AsDateTime := I;
          Open;
    End;
End; 

Answer 4

Var
  I: TDate;
  TableName: String;
Begin
    Begin
       query1.SQL.Clear;
       query1.SQL.Add('Select * From '+TableName);
       query1.SQL.Add('Where Start_Day = :day');
       query1.ParamByName('dqy').AsDateTime := I;
       query1.Open;
    End;

Answer 5

真的很感谢各位，本来抱着试一试的心理来这里请教，想不到还真得到了答案，我是DELPHI新手，看来我加入这个栏目是对的。全都给分！

Answer 6

query.add('select * from tablename where start_day='''+datetostr(i)+'''');