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)
	}
}

// evalNode on a literal value is independent of the node being an
// aggregation or a row function - it always returns a value.