Coalesce function replacing in ClickHouse - clickhouse

Question

I'm beginner in ClickHouse and trying to use for handling statistic of our project. Some desktop software send information to our servers and we need to group operation systems to short list. This example query:
SELECT OS
FROM Req
GROUP BY OS
┌─OS──────────────────────────────────────────────────────────────────────────────┐
│ Майкрософт Windows 10 Корпоративная 2016 с долгосрочным обслуживанием │
│ Майкрософт Ознакомительная версия Windows Server 2012 Standard │
│ Майкрософт Windows 10 Домашняя для одного языка │
│ Microsoft Windows 8.1 Enterprise │
│ Майкрософт Windows 8 Корпоративная Прогрессивная │
│ Microsoft Windows Server 2008 R2 Standard │
│ Microsoft Windows 8.1 mit Bing │
│ Microsoft Windows 10 Home │
│ Microsoft Windows 8 Enterprise N │
│ Майкрософт Windows 8.1 Профессиональная │
│ Майкрософт Windows 8 Профессиональная │
│ Microsoft Windows 7 Rеактивная │
│ Microsoft Windows 10 Pro Insider Preview │
need to be aggregate to clean list:
8 xxx
8.1 yyy
2008 zzz
2008 R2 aaa
and so on. I'm not found COALESCE function and try to using extract for identify OS by version numbers:
select extract(OS, ' 7 ') || extract(OS, ' 8.1 ') || extract(OS, ' 10 ') || extract(OS, ' 2008 R2 ') || extract (OS, ' 2008 ') || extract(OS, ' 2012 R2 ') || extract(OS, ' 2012 ') as Value, count(distinct SID) from Req group by Value limit 100000;
But! Because Windows 2008 and Windows 2008 R2 have '2008' in version string, i'm received this result:
┌─Value───────────┬─uniqExact(SID)─┐
│ │ 224 │
│ 2012 │ 17 │
│ 10 │ 1315 │
│ 7 │ 4282 │
│ 2008 │ 20 │
│ 2012 R2 2012 │ 57 │
│ 2008 R2 2008 │ 136 │
│ 8.1 │ 754 │
└─────────────────┴────────────────┘
What function I need to be use in my case? Thanks.

Answer 1

What you need here is a multif.
If the string "2012 R2" is found, return me that, if "2012" return me that... etc.
so in your case you could do something like this:
multiIf(like(OS, '% 2008 R2 %'), extract(OS, ' 2008 R2 ') , like(OS, '% 2008 %'), extract (OS, ' 2008 '), 'OS_not_found') as Value
This is basically an if else if and you can add as many values as you like, I just used the two because I didn't want to write too much, but in your case just add all the OS values you need. Its a bit verbose but it gets the job done.
The function:
like(OS, '% 2008 R2 %')
returns true if the string is found and false otherwise, the "%" is the regex wildcard in clickhouse. Since the multif stops at the first match you will not get two extracted string in the same value.

Answer 2

Found!
select OS, arrayFirst(x -> cast(position(OS, x) as UInt8), [' 8 ',' 8.1 ', '2008 R2', '2008'])
from Req
limit 1000;
(without CAST i'm receive exeption: DB::Exception: Unexpected type of filter column., strange...)