`SELECT ... WHERE match(key, '^prefix...')`
should use index similarly to
`SELECT ... WHERE key LIKE 'prefix%'`
else if (element.function == RPNElement::FUNCTION_AND)
        {
            assert(!rpn_stack.empty());
            auto arg1 = rpn_stack.back();
            rpn_stack.pop_back();
            auto arg2 = rpn_stack.back();
            rpn_stack.back() = arg1 & arg2;
        }
        else if (element.function == RPNElement::FUNCTION_OR)
        {
            assert(!rpn_stack.empty());
            auto arg1 = rpn_stack.back();
            rpn_stack.pop_back();
            auto arg2 = rpn_stack.back();
            rpn_stack.back() = arg1 | arg2;
        }
        else
            throw Exception("Unexpected function type in KeyCondition::RPNElement", ErrorCodes::LOGICAL_ERROR);
    }
    if (rpn_stack.size() != 1)
        throw Exception("Unexpected stack size in KeyCondition::unknownOrAlwaysTrue", ErrorCodes::LOGICAL_ERROR);
    return rpn_stack[0];
}
bool KeyCondition::alwaysFalse() const
{
    
    std::vector<UInt8> rpn_stack;
    for (const auto & element : rpn)
    {
        if (element.function == RPNElement::ALWAYS_TRUE)