**Describe the situation**

Currently it does not:

```
milovidov-desktop :) EXPLAIN SYNTAX SELECT sum(cityHash64(*)) AS x FROM test.hits WHERE URLDomain LIKE '%metrika%'

EXPLAIN SYNTAX
SELECT sum(cityHash64(*)) AS x
FROM test.hits
WHERE URLDomain LIKE '%metrika%'

Query id: a752ed76-a71c-4e26-96c1-1b081abfc539

┌─explain────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ SELECT sum(cityHash64(WatchID, JavaEnable, Title, GoodEvent, EventTime, EventDate, CounterID, ClientIP, ClientIP6, RegionID, UserID, CounterClass, OS, UserAgent, URL, Referer, URLDomain, RefererDomain, Refresh, IsRobot, RefererCategories, URLCategories, URLRegions, RefererRegions, ResolutionWidth, ResolutionHeight, ResolutionDepth, FlashMajor, FlashMinor, FlashMinor2, NetMajor, NetMinor, UserAgentMajor, UserAgentMinor, CookieEnable, JavascriptEnable, IsMobile, MobilePhone, MobilePhoneModel, Params, IPNetworkID, TraficSourceID, SearchEngineID, SearchPhrase, AdvEngineID, IsArtifical, WindowClientWidth, WindowClientHeight, ClientTimeZone, ClientEventTime, SilverlightVersion1, SilverlightVersion2, SilverlightVersion3, SilverlightVersion4, PageCharset, CodeVersion, IsLink, IsDownload, IsNotBounce, FUniqID, HID, IsOldCounter, IsEvent, IsParameter, DontCountHits, WithHash, HitColor, UTCEventTime, Age, Sex, Income, Interests, Robotness, GeneralInterests, RemoteIP, RemoteIP6, WindowName, OpenerName, HistoryLength, BrowserLanguage, BrowserCountry, SocialNetwork, SocialAction, HTTPError, SendTiming, DNSTiming, ConnectTiming, ResponseStartTiming, ResponseEndTiming, FetchTiming, RedirectTiming, DOMInteractiveTiming, DOMContentLoadedTiming, DOMCompleteTiming, LoadEventStartTiming, LoadEventEndTiming, NSToDOMContentLoadedTiming, FirstPaintTiming, RedirectCount, SocialSourceNetworkID, SocialSourcePage, ParamPrice, ParamOrderID, ParamCurrency, ParamCurrencyID, GoalsReached, OpenstatServiceName, OpenstatCampaignID, OpenstatAdID, OpenstatSourceID, UTMSource, UTMMedium, UTMCampaign, UTMContent, UTMTerm, FromTag, HasGCLID, RefererHash, URLHash, CLID, YCLID, ShareService, ShareURL, ShareTitle, `ParsedParams.Key1`, `ParsedParams.Key2`, `ParsedParams.Key3`, `ParsedParams.Key4`, `ParsedParams.Key5`, `ParsedParams.ValueDouble`, IslandID, RequestNum, RequestTry)) AS x │
│ FROM test.hits                                                                                                                                                                                                                                             │
│ PREWHERE URLDomain LIKE '%metrika%'                                                                                                                                                                                                                        │
└────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

3 rows in set. Elapsed: 0.004 sec. 

milovidov-desktop :) EXPLAIN SYNTAX SELECT sum(cityHash64(*)) AS x FROM merge(test, '^hits$') WHERE URLDomain LIKE '%metrika%'

EXPLAIN SYNTAX
SELECT sum(cityHash64(*)) AS x
FROM merge(test, '^hits$')
WHERE URLDomain LIKE '%metrika%'

Query id: fb059673-7da1-4cf4-9713-e5c7b9feb66d

┌─explain────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ SELECT sum(cityHash64(WatchID, JavaEnable, Title, GoodEvent, EventTime, EventDate, CounterID, ClientIP, ClientIP6, RegionID, UserID, CounterClass, OS, UserAgent, URL, Referer, URLDomain, RefererDomain, Refresh, IsRobot, RefererCategories, URLCategories, URLRegions, RefererRegions, ResolutionWidth, ResolutionHeight, ResolutionDepth, FlashMajor, FlashMinor, FlashMinor2, NetMajor, NetMinor, UserAgentMajor, UserAgentMinor, CookieEnable, JavascriptEnable, IsMobile, MobilePhone, MobilePhoneModel, Params, IPNetworkID, TraficSourceID, SearchEngineID, SearchPhrase, AdvEngineID, IsArtifical, WindowClientWidth, WindowClientHeight, ClientTimeZone, ClientEventTime, SilverlightVersion1, SilverlightVersion2, SilverlightVersion3, SilverlightVersion4, PageCharset, CodeVersion, IsLink, IsDownload, IsNotBounce, FUniqID, HID, IsOldCounter, IsEvent, IsParameter, DontCountHits, WithHash, HitColor, UTCEventTime, Age, Sex, Income, Interests, Robotness, GeneralInterests, RemoteIP, RemoteIP6, WindowName, OpenerName, HistoryLength, BrowserLanguage, BrowserCountry, SocialNetwork, SocialAction, HTTPError, SendTiming, DNSTiming, ConnectTiming, ResponseStartTiming, ResponseEndTiming, FetchTiming, RedirectTiming, DOMInteractiveTiming, DOMContentLoadedTiming, DOMCompleteTiming, LoadEventStartTiming, LoadEventEndTiming, NSToDOMContentLoadedTiming, FirstPaintTiming, RedirectCount, SocialSourceNetworkID, SocialSourcePage, ParamPrice, ParamOrderID, ParamCurrency, ParamCurrencyID, GoalsReached, OpenstatServiceName, OpenstatCampaignID, OpenstatAdID, OpenstatSourceID, UTMSource, UTMMedium, UTMCampaign, UTMContent, UTMTerm, FromTag, HasGCLID, RefererHash, URLHash, CLID, YCLID, ShareService, ShareURL, ShareTitle, `ParsedParams.Key1`, `ParsedParams.Key2`, `ParsedParams.Key3`, `ParsedParams.Key4`, `ParsedParams.Key5`, `ParsedParams.ValueDouble`, IslandID, RequestNum, RequestTry)) AS x │
│ FROM merge('test', '^hits$')                                                                                                                                                                                                                               │
│ WHERE URLDomain LIKE '%metrika%'                                                                                                                                                                                                                           │
└────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
```

Most likely because Merge table does not provide column sizes info.
We can provide it either:
- by iterating and summing across all tables;
- only for first N = 10 tables in case if the number of tables is very large.
if (alias_columns_required)
    {
        NameSet required_columns_from_prewhere; 
        NameSet required_aliases_from_prewhere; 
        if (prewhere_info)
        {
            
            auto prewhere_required_columns = prewhere_info->prewhere_actions->getRequiredColumns().getNames();
            required_columns_from_prewhere.insert(prewhere_required_columns.begin(), prewhere_required_columns.end());
            if (prewhere_info->row_level_filter)
            {
                auto row_level_required_columns = prewhere_info->row_level_filter->getRequiredColumns().getNames();
                required_columns_from_prewhere.insert(row_level_required_columns.begin(), row_level_required_columns.end());
            }
        }
        
        ASTPtr required_columns_all_expr = std::make_shared<ASTExpressionList>();
        
        ASTPtr required_columns_from_prewhere_expr = std::make_shared<ASTExpressionList>();
        
        
        for (const auto & column : required_columns)
        {
            ASTPtr column_expr;