if lerr != nil || len(e.Right) == 0 {
		return lval, lerr
	}

	// Process remaining child nodes - result must be
	// numeric. This AST node is for terms separated by + or -
	// symbols.
	for _, rightTerm := range e.Right {
		op := rightTerm.Op
		rval, rerr := rightTerm.Right.evalNode(r, tableAlias)
		if rerr != nil {
			return nil, rerr
		}
		err := lval.arithOp(op, rval)