parameters FDquery delphi does not work

Question

i have the following delphi code:

FDQuery1.SQL.Clear;
FDQuery1.SQL.Add('SELECT * FROM :Tablename');
FDQuery1.ParamByName('Tablename').AsString := 'tasks';
ShowMessage(FDQuery1.sql.Text);
FDQuery1.Open;

(coppied from this link: http://www.delphigroups.info/2/da/237634.html )

it does not work because the parameter is not filled but stays the same. does somebody know why it is not filled?

Answer 1

Because you cannot use parameters for table name substitution in SQL commands in general. You are lucky enough here though, FireDAC supports preprocessor macros to parametrize table names in SQL commands. So you can write for example this (note that if you want to see the command as you did in your code, it must be after macro preprocessing, that is eg after calling Prepare ):

FDQuery1.SQL.Text := 'SELECT * FROM &TableName';
FDQuery1.MacroByName('TableName').AsIdentifier := 'tasks';
FDQuery1.Open;

For details about this kind of macros, see the substitution variables topic.