func (e *FuncExpr) evalAggregationNode(r Record, tableAlias string) error {
	// It is assumed that this function is called only when
	// `e` is an aggregation function.

	var val *Value
	var err error
	funcName := e.getFunctionName()
	if aggFnCount == funcName {
		if e.Count.StarArg {
			// Handle COUNT(*)
			e.aggregate.runningCount++
			return nil
		}

		val, err = e.Count.ExprArg.evalNode(r, tableAlias)
		if err != nil {

		result = e.FuncCall.analyze(s)

	default:
		result = qProp{err: errUnexpectedInvalidNode}
	}
	return
}

func (e *FuncExpr) analyze(s *Select) (result qProp) {
	funcName := e.getFunctionName()

	switch funcName {
	case sqlFnCast:
		return e.Cast.Expr.analyze(s)

	case sqlFnExtract:
		return e.Extract.From.analyze(s)

	case sqlFnDateAdd:

	case e.FuncCall != nil:
		return e.FuncCall.evalNode(r, tableAlias)
	}
	return nil, errInvalidASTNode
}

func (e *FuncExpr) evalNode(r Record, tableAlias string) (res *Value, err error) {
	switch e.getFunctionName() {
	case aggFnCount, aggFnAvg, aggFnMax, aggFnMin, aggFnSum:
		return e.getAggregate()
	default:
		return e.evalSQLFnNode(r, tableAlias)
	}
}