loop in Table

You need to formulate the problem more precisely, for example:
I need a button to cycle through data in a table, so that the desired value in a specified field moves through the records (rows on the screen) from the beginning to the end, and then back to the beginning.
If this is what you need, then let me clarify: should the result of the “movement” be saved in the database or will it be relevant only during a program session? That is, you need to “move” the data in a table view on the screen or in a database table?

procedure Form1_Button1_OnClick (Sender: TObject; var Cancel: boolean);
var
  ID : String;
  NextID : String;
begin
  ID := SQLExecute('SELECT id FROM myData WHERE toAdd = 0') ;
  NextID := SQLExecute('SELECT id FROM myData WHERE id > '+ID+' ORDER BY id LIMIT 1' ) ;
  if NextID = '' then
    NextID := SQLExecute('SELECT id FROM myData ORDER BY id LIMIT 1' ) ;
  SQLExecute('UPDATE myData SET toAdd = NULL where id = '+ID ) ;
  SQLExecute('UPDATE myData SET toAdd = 0 where id = '+NextID ) ;
  Form1.TableGrid1.dbUpdate;
end;

The procedure moves the data to the toAdd field, using the ID field as the serial number

Hi Lara, Konstantin,
If I understand the question correctly (an identical calculation for all rows in a table with the result added to a "result" column), perhaps this will do what you want (attached is a simple example).
Derek.

Hi,
The conventional way is to load all the data into a tablegrid and then loop through each row and perform whatever calculations / checks you need.
Have a look at the attachment which gets a 'discount rate' from a look-up table and calculates a 'sale price' for each item in the 'items' table.
You can then either 'clear' the 'sale price' or change the 'discount rates' and then recalculate the 'sale prices' etc etc.
Obviously there are other checks and controls you would want to put in place but this is just to show you the basics.
Derek.