这个SQL语句哪有问题？

Question

select * from vok where vname ="'+S_Vistor+'" and  DATEDIFF ("day",'+datetostr(S_Date)+',vtime)<2

Answer 1

var
sqlstr:string;
begin
sqlstr:='select * from vok where vname ='''+S_Vistor+''' and  DATEDIFF (day,'''+datetostr(S_Date)+''',vtime) <2';
....
end;

Answer 2

select * from vok where vname ='S_Vistor' and  DATEDIFF ('day','datetostr(S_Date)',vtime) <2

Answer 3

   adoquery1.sql.Add('select * from vok where vname ='''+S_Vistor+''' and  DATEDIFF (day,'''+datetostr(S_Date)+''','''+vtime+''') <2');

Answer 4

引号多了看着费劲，习惯使用ParamByName(paramname).value

Answer 5

用QuotedStr吧，这样最易读，而且以后移植也方便`!