docs: private static AbstractExpression addScalarValueExpression(SelectSubqueryExpression expr) {
          if (expr.getSubqueryScan().getOutputSchema().size() != 1) {
              throw new PlanningErrorException("Scalar subquery can have only one output column");
          }
  
          expr.changeToScalarExprType();
  
          AbstractExpression scalarExpr = new ScalarValueExpression();
          scalarExpr.setLeft(expr);
          scalarExpr.setValueType(expr.getValueType());
          scalarExpr.setValueSize(expr.getValueSize());
          return scalarExpr;
      }