求助--在线等----从字元字串转换到datetime时，转换失败

[feiaizhong]

var
st: string;
et: String;



st:=datetostr(datetimepicker1.date)+' '+FormatDateTime('hh:nn:ss',DateTimePicker2.DateTime);
et:=datetostr(datetimepicker3.date)+' '+FormatDateTime('hh:nn:ss',DateTimePicker4.DateTime);


sqlstr :='select w.csno as SN,w.macno as macAddress,s.model,s.cdt AS Date,c.wcname as TestStation, '
+' (case s.ispass when 0 then '+Quotedstr('FAIL')+' else '+Quotedstr('PASS')+' end) as [TestResult], '
+' (case s.ispass when 0 then f.defect else '+Quotedstr('')+' end) as [FailCode], '
+' (case s.ispass when 0 then d.doc else '+Quotedstr('')+' end) as [FailureReason],'+Quotedstr('')+' as DefectType,'+Quotedstr('')+' as RefDes,'+Quotedstr('Sercomm')+' as [ODM] '
+' from sfc_log s with(nolock) '
+' full join wosn09 w with(nolock) '
+' on w.pcb + w.isno = s.isno '
+' full join wc c with(nolock) '
+' on s.wcno = c.wcno '
+' full join sfc_dftm d with(nolock) '
+' on s.isno = d.isno '
+' full join defect f with(nolock) '
+' on d.defect = f.defect '
+' where s.cdt>='+Quotedstr('st') +'and s.cdt <='+Quotedstr('et')+ 'and w.macno <>'+Quotedstr('');

with ADOQuery1 do
begin
ADOQuery1.close;
ADOQuery1.sql.Clear;
ADOQuery1.sql.Add(sqlstr);
ADOQuery1.open;
label4.Caption:='共找到'+inttostr(adoquery1.RecordCount)+'条记录。';
end;


执行的时候总是提示“从字元字串转换到datetime时，转换失败”
请问WHERE后面的条件该如何修改？

[starluck]

var 
st: string; 
et: String; 


st:=datetostr(datetimepicker1.date)+' '+FormatDateTime('hh:nn:ss',DateTimePicker2.DateTime); 
et:=datetostr(datetimepicker3.date)+' '+FormatDateTime('hh:nn:ss',DateTimePicker4.DateTime); 


sqlstr :='select w.csno as SN,w.macno as macAddress,s.model,s.cdt AS Date,c.wcname as TestStation,  ' 
          +'  (case s.ispass when 0 then '+Quotedstr('FAIL')+' else '+Quotedstr('PASS')+' end) as [TestResult],  ' 
          +'  (case s.ispass when 0 then f.defect else '+Quotedstr('')+' end) as [FailCode], ' 
          +'        (case s.ispass when 0 then d.doc else '+Quotedstr('')+' end)  as [FailureReason],'+Quotedstr('')+' as DefectType,'+Quotedstr('')+' as RefDes,'+Quotedstr('Sercomm')+' as [ODM]  ' 
          +'  from sfc_log s with(nolock)  ' 
          +'  full join wosn09 w with(nolock)  ' 
          +'  on w.pcb + w.isno = s.isno  ' 
          +'  full join wc c with(nolock) ' 
          +'  on s.wcno = c.wcno ' 
          +'  full join sfc_dftm d with(nolock) ' 
          +'  on s.isno = d.isno  ' 
          +'  full join defect f with(nolock) ' 
          +'  on d.defect = f.defect ' 
          +'  where s.cdt>='+Quotedstr(ST) +'and s.cdt <='+Quotedstr(ET)+ 'and w.macno <>'+Quotedstr(''); 

with ADOQuery1 do 
begin 
ADOQuery1.close; 
ADOQuery1.sql.Clear; 
ADOQuery1.sql.Add(sqlstr); 
ADOQuery1.open; 
label4.Caption:='共找到'+inttostr(adoquery1.RecordCount)+'条记录。'; 
end; 

[starluck]

var 
st: string; 
et: String; 


st:=datetostr(datetimepicker1.date)+' '+FormatDateTime('hh:nn:ss',DateTimePicker2.DateTime); 
et:=datetostr(datetimepicker3.date)+' '+FormatDateTime('hh:nn:ss',DateTimePicker4.DateTime); 


sqlstr :='select w.csno as SN,w.macno as macAddress,s.model,s.cdt AS Date,c.wcname as TestStation,  ' 
          +'  (case s.ispass when 0 then '+Quotedstr('FAIL')+' else '+Quotedstr('PASS')+' end) as [TestResult],  ' 
          +'  (case s.ispass when 0 then f.defect else '+Quotedstr('')+' end) as [FailCode], ' 
          +'        (case s.ispass when 0 then d.doc else '+Quotedstr('')+' end)  as [FailureReason],'+Quotedstr('')+' as DefectType,'+Quotedstr('')+' as RefDes,'+Quotedstr('Sercomm')+' as [ODM]  ' 
          +'  from sfc_log s with(nolock)  ' 
          +'  full join wosn09 w with(nolock)  ' 
          +'  on w.pcb + w.isno = s.isno  ' 
          +'  full join wc c with(nolock) ' 
          +'  on s.wcno = c.wcno ' 
          +'  full join sfc_dftm d with(nolock) ' 
          +'  on s.isno = d.isno  ' 
          +'  full join defect f with(nolock) ' 
          +'  on d.defect = f.defect ' 
          +'  where s.cdt>='+Quotedstr(ST) +'  and s.cdt <='+Quotedstr(ET)+ '  and w.macno <>'+Quotedstr(''); 

with ADOQuery1 do 
begin 
ADOQuery1.close; 
ADOQuery1.sql.Clear; 
ADOQuery1.sql.Add(sqlstr); 
ADOQuery1.open; 
label4.Caption:='共找到'+inttostr(adoquery1.RecordCount)+'条记录。'; 
end; 

[bdmh]

ST,ET是变量,就不要再加引号了

[bdmh]

如果s.cdt是日期型字段,那就不用加引号了

'  where s.cdt>='+st+' and s.cdt <='+et+ 'and w.macno <>'+Quotedstr(''); 

[feiaizhong]

明白，已经搞定了，谢谢楼上的朋友们！