Convert SQL server query to Delphi syntax

This is the original SQL server query which works:

use HIS

SELECT
room_type,rate_start_date,rate_end_date,rate
, DATEDIFF(DAY,case when rate_end_date < '2011.08.21'
then '2011.08.19'
else rate_start_date
end,
case when rate_start_date > '2011.08.19'
then '2011.08.21'
else rate_end_date
end
) AS days FROM room_rates
WHERE room_type = 'DBLMS' AND rate_start_date <= '2011.08.21'
AND rate_end_date > '2011.08.19'

I converted it to Delphi SQL :

procedure TForm1.Button1Click(Sender: TObject);
begin
uniQuery1.Close;
uniQuery1.SQL.Clear;
uniQuery1.SQL.Add('SELECT room_type,rate_start_date,rate_end_date,rate,');
uniQuery1.SQL.Add('DATEDIFF(DAY,case when rate_end_date < 2011.08.21 then 2011.08.19 else rate_start_date end,');
uniQuery1.SQL.Add('case when rate_start_date > 2开发者_高级运维011.08.19');
uniQuery1.SQL.Add('then 2011.08.21 else rate_end_date end) AS days FROM room_rates');
uniQuery1.SQL.Add('WHERE room_type = DBLMS AND rate_start_date <= 2011.08.21');
uniQuery1.SQL.Add('AND rate_end_date > 2011.08.19');
uniQuery1.Open;
end;

However I am getting 'Invalid column NAME 'DBLMS''

What am I missing here ? DBLMS is not a column.

You are no quoting the strings inside of your sql sentence try rewriting your code to this :

procedure TForm1.Button1Click(Sender: TObject);
begin
  uniQuery1.Close;
  uniQuery1.SQL.Clear;
  uniQuery1.SQL.Add('SELECT room_type,rate_start_date,rate_end_date,rate,');
  uniQuery1.SQL.Add('DATEDIFF(DAY,case when rate_end_date < ''2011.08.21'' then ''2011.08.19'' else rate_start_date end,');
  uniQuery1.SQL.Add('case when rate_start_date > ''2011.08.19''');
  uniQuery1.SQL.Add('then ''2011.08.21'' else rate_end_date end) AS days FROM room_rates');
  uniQuery1.SQL.Add('WHERE room_type = ''DBLMS'' AND rate_start_date <= ''2011.08.21''');
  uniQuery1.SQL.Add('AND rate_end_date > ''2011.08.19''');
  uniQuery1.Open;
end;

As addtional advice , try using parameters instead of string literals, in this way you will protect your code against sql injection beside others advantages. check this article Using Parameters in Queries