How to FindNearest

How to implement the functionality similar to the BDE/Paradox TTable.FindNearest?

Suppose we have huge table. On the screen we need to show contents of that table in the Grid and under that Grid user can input in TextBox some letters. OnChange of this TextBox we need to make current row selection in the Grid on the row with value of some column nearest to the user input in the TextBox.

How this can be implemented in PostgreSQL?

At my first sight:
I found there is CURSOR functionality which can move that cursor through the ResultSet. But we can move it just relatively phisical row number. Is there any chance to make cursor move to the row by some rule based on the row values?

All possible approaches and ideas highly appreciated. There is just one requirement - the performance, it should work as fast as possible.

Regards,
Alexander Ilyin