The only way to use this feature is to specify an empty database name in Distributed table definition, but then you get a warning:

```
CREATE TABLE `demo_loan_all` (...) ENGINE=Distributed(test_cluster_two_shards_different_databases, '', demo_loan_01568, cityHash64(id));

<Warning> StorageDistributed (demo_loan_all): Name of remote database is empty. Default database will be used implicitly.
```
throw Exception("optimize_skip_unused_shards_limit out of range (0, {}]", ErrorCodes::ARGUMENT_OUT_OF_BOUND, SSIZE_MAX);
    }
    
    ++limit;
    const auto blocks = evaluateExpressionOverConstantCondition(condition_ast, sharding_key_expr, limit);
    if (!limit)
    {
        LOG_TRACE(log,
            "Number of values for sharding key exceeds optimize_skip_unused_shards_limit={}, "
            "try to increase it, but note that this may increase query processing time.",
            local_context->getSettingsRef().optimize_skip_unused_shards_limit);
        return nullptr;
    }
    
    if (!blocks)
    {
        return nullptr;
    }
    std::set<int> shards;
    for (const auto & block : *blocks)
    {
        if (!block.has(sharding_key_column_name))
            throw Exception("sharding_key_expr should evaluate as a single row", ErrorCodes::TOO_MANY_ROWS);
        const ColumnWithTypeAndName & result = block.getByName(sharding_key_column_name);
        const auto selector = createSelector(cluster, result);
        shards.insert(selector.begin(), selector.end());
    }
    return cluster->getClusterWithMultipleShards({shards.begin(), shards.end()});
}
ActionLock StorageDistributed::getActionLock(StorageActionBlockType type)