a #GdaConnection object, or null
parameters contained in a single #GdaSet object, or null
a set of flags to control the rendering
a place to store the list of actual #GdaHolder objects in params used to do the rendering, or null
a new string if no error occurred
Renders stmt as an SQL statement, with some control on how it is rendered.
If cnc is not null, then the rendered SQL will better be suited to be used by cnc (in particular it may include some SQL tweaks and/or proprietary extensions specific to the database engine used by cnc): in this case the result is similar to calling gda.connection.Connection.statementToSql.