FYI:

The filter string for TFDTable must be (with {fn } for substring):

TFDTable.Filter := ({fn SUBSTRING( {id COL1}, 6, 1)} = {s 4} )

The filter string for TFDQuery can be: (without {fn } for substring) -- This doesn't work for TFDTable!

TFDQuery.Filter := (SUBSTRING( {id TYP}, 6, 1) = {s 4})

Thanks
Norbert