query works on sql server management studio 2008 but not in delphi

Question

I'm developing a program to update some fields in a table in delphi 7 using sql server. the program goes like this:

sql := 'UPDATE tb_dt_contract SET '
      +' id_schedule = '+quotedstr(label_id_schedule.Caption)
      +',start_date = '+quotedstr(formatdatetime('mm/dd/yyyy',DateTime_start.Date))
      +',finish_date = '+quotedstr(formatdatetime('mm/dd/yyyy',DateTime_finish.Date))
      +',contract_location = '+quotedstr(uppercase(Edit_location.Text))
      +',sign_date = '+quotedstr(formatdatetime('mm/dd/yyyy',DateTime_sign.Date))
      +' WHERE id = '+quotedstr(label_id.Caption);
ADOQuery1.Close;
ADOQuery1.SQL.Text := sql;
ADOQuery1.ExecSQL;

when I run the program, it gives me an error: 'Incorrect syntax near '=''. but when I use showmessage to view the query and run it in sql server management 2008, it works fine.

then I try to split the query into parts like this:

SQL := 'UPDATE tb_dt_contract SET '
      +' id_schedule = '+QUOTEDSTR(label_id_schedule.CAPTION)
      +' WHERE id = '+quotedstr(label_id.Caption);
ADOQuery1.Close;
ADOQuery1.SQL.Text := sql;
ADOQuery1.ExecSQL;

SQL := 'UPDATE tb_dt_contract SET '
      +' start_date = '+quotedstr(formatdatetime('mm/dd/yyyy',DateTime_start.Date))
      +' WHERE id = '+quotedstr(label_id.Caption);
ADOQuery1.Close;
ADOQuery1.SQL.Text := sql;
ADOQuery1.ExecSQL;

SQL := 'UPDATE tb_dt_contract SET '
      +' finish_date = '+quotedstr(formatdatetime('mm/dd/yyyy',DateTime_finish.Date))
      +' WHERE id = '+quotedstr(label_id.Caption);
ADOQuery1.Close;
ADOQuery1.SQL.Text := sql;
ADOQuery1.ExecSQL;

SQL := 'UPDATE tb_dt_contract SET '
      +' contract_location = '+quotedstr(uppercase(edit_location.Text))
      +' WHERE id = '+quotedstr(label_id.Caption);
ADOQuery1.Close;
ADOQuery1.SQL.Text := sql;
ADOQuery1.ExecSQL;

SQL := 'UPDATE tb_dt_contract SET '
      +' sign_date = '+quotedstr(formatdatetime('mm/dd/yyyy',DateTime_sign.Date))
      +' WHERE id = '+quotedstr(label_id.Caption);
ADOQuery1.Close;
ADOQuery1.SQL.Text := sql;
ADOQuery1.ExecSQL;

then I found out that it only triggers the error when updating a date type field. I have developed other programs to update different tables using similar query and it works fine.. I tried closing the project and reopening it but it still gives me that error message. please tell me what I should do..

Answer 1

To avoid convertions and create database independed save querys you should use parameters, which also could speed up operations if used more than once.

  Adoquery1.SQL.Text := 'UPDATE tb_dt_contract SET finish_date=:df where WHERE id =:id';
  // in some cases it may be necessary to add  the three comented lines
  //Adoquery1.Parameters.ParseSQL(Adoquery1.SQL.Text,true);
  //Adoquery1.Parameters.ParamByName('df').DataType := ftDateTime;
  //Adoquery1.Parameters.ParamByName('id').DataType := ftInteger;
  Adoquery1.Parameters.ParamByName('df').Value :=DateTime_finish.Date;
  Adoquery1.Parameters.ParamByName('ID').Value :=StrToInt(label_id.Caption);
  Adoquery1.ExecSQL;