private static bool IsNullableProjection(ProjectionExpression projectionExpression)
 => projectionExpression.Expression switch
 {
 internal ColumnExpression(ProjectionExpression subqueryProjection, TableExpressionBase table)
     : this(subqueryProjection.Alias, table,
            subqueryProjection.Type, subqueryProjection.Expression.TypeMapping,
            IsNullableProjection(subqueryProjection))
 {
 }