`SELECT ... WHERE match(key, '^prefix...')`
should use index similarly to
`SELECT ... WHERE key LIKE 'prefix%'`
{
    try
    {
        src_value = convertFieldToType(src_value, *desired_type, src_type.get());
    }
    catch (...)
    {
        throw Exception("Key expression contains comparison between inconvertible types: " +
            desired_type->getName() + " and " + src_type->getName() +
            " inside " + node.getColumnName(),
            ErrorCodes::BAD_TYPE_OF_FIELD);
    }
}
bool KeyCondition::tryParseAtomFromAST(const Tree & node, ContextPtr context, Block & block_with_constants, RPNElement & out)
{
    /** Functions < > = != <= >= in `notIn` isNull isNotNull, where one argument is a constant, and the other is one of columns of key,
      *  or itself, wrapped in a chain of possibly-monotonic functions,
      *  or constant expression - number.
      */
    Field const_value;
    DataTypePtr const_type;
    if (node.isFunction())
    {
        auto func = node.asFunction();
        size_t num_args = func.numArguments();
        DataTypePtr key_expr_type;    
        size_t key_column_num = -1;   
        MonotonicFunctionsChain chain;
        std::string func_name = func.getFunctionName();