public SqlExpression Prepare(SqlExpression expression) { var refName = ((SqlReferenceExpression)expression).ReferenceName; var reference = fromSet.QualifyReference(refName); if (reference is ObjectName) { return(SqlExpression.Reference((ObjectName)reference)); } if (reference is QueryReference) { return(new QueryReferenceExpression((QueryReference)reference)); } throw new InvalidOperationException(); }