public function walkCoalesceExpression($coalesceExpression)
    {
        $sql = 'COALESCE(';

        $scalarExpressions = [];

        foreach ($coalesceExpression->scalarExpressions as $scalarExpression) {
            $scalarExpressions[] = $this->walkSimpleArithmeticExpression($scalarExpression);
        }

        return $sql . implode(', ', $scalarExpressions) . ')';
    }