code: protected AbstractColumn buildExpressionColumn() {
  		ExpressionColumn column = new ExpressionColumn();
  		populateCommonAttributes(column);
  		
  		populateExpressionAttributes(column);
  		
  		column.setExpression(customExpression);
  		column.setExpressionToGroupBy(customExpressionToGroupBy);
  		column.setExpressionForCalculation(customExpressionForCalculation);
  		
  		return column;
  	}
docs: For creating expression columns
  @return