Parameter Markers

Parameter markers, including parameter markers for stored procedures, are specified in the ADO.NET data provider by using the "?" symbol in SQL statements.

UPDATE emp SET job = ?, sal = ? WHERE empno = ?

Because parameters are not named, the bindings must occur in the order of the parameters in the statement. This means that the calls to the Add() method on the PsqlParameterCollection object (adding the Parameter objects to the collection) must occur in the order of the "?"s in the command text.