Multi-part identifier leads to problems in MSSQL

**Describe the bug**
When using the library against a MSSQL database, the created SQL statement leads to an error, because the alias "c" is used multible times for subselects. This is allowed in postgres, but MSSQL is more strict.

**To Reproduce**
Currently the code is run by an other R-Project. My knowlege in R is very limited, so I can not provide a good example.

**Expected behavior**

Instead of using the same alias in the subselects (here orignall always c) use different (like c1, c2, ...) : the following statement also workds for MSSQL

SELECT 0 as codeset_id, c.concept_id
FROM (
select distinct I.concept_id
FROM (
select concept_id
from "digione".CONCEPT
where (concept_id in (4162253,36564848,4092513,4158563,4158563,4187850,4187851,4188545, 4237178,441513,44502548,4221403,4295715))
UNION
select c1.concept_id
from "digione".CONCEPT c1
join "digione".CONCEPT_ANCESTOR ca on c1.concept_id = ca.descendant_concept_id
WHERE c1.invalid_reason is null and (ca.ancestor_concept_id in (4162253,36564848,4092513,4158563,4158563,4187850,4187851,4188545,4237178,441513,44502548,4221403,4295715)) ) I
LEFT JOIN (
select concept_id from "digione".CONCEPT
where (concept_id in (4147164,139750,4162276,1075593,36712738,36712739))
UNION select c2.concept_id from "digione".CONCEPT c2 join "digione".CONCEPT_ANCESTOR ca on
c2.concept_id = ca.descendant_concept_id WHERE c2.invalid_reason is null
and (ca.ancestor_concept_id in (4147164,139750,4162276,1075593,36712738,36712739)) ) E
ON I.concept_id = E.concept_id WHERE E.concept_id is null ) c;

**Screenshots**
no screenshot, but the generated SQL-Statement and stack trace

Backtrace:

9. ├─CDMConnector::generateCohortSet(...) at DigiONE04-Flat-file-generation/R/0_CohortGeneration.R:36:1
10. │ └─CDMConnector (local) generate(i) at CDMConnector/R/generateCohortSet.R:581:5
11. │ ├─DBI::dbExecute(con, sql[k], immediate = TRUE) at CDMConnector/R/generateCohortSet.R:570:7
12. │ └─DBI::dbExecute(con, sql[k], immediate = TRUE) at DBI/R/dbExecute.R:57:3
13. │ └─odbc (local) .local(conn, statement, ...)
14. │ ├─DBI::dbSendStatement(conn, statement, params = params, ..., immediate = immediate)
15. │ └─odbc::dbSendStatement(...)
16. │ └─odbc (local) .local(conn, statement, ...)
17. │ └─odbc:::OdbcResult(...)
18. │ └─odbc:::new_result(p = connection@ptr, sql = statement, immediate = immediate)
19.
The multi-part identifier "c.concept_id" could not be bound. •
INSERT INTO #Codesets (codeset_id, concept_id)
SELECT 0 as codeset_id, c.concept_id
FROM (
select distinct I.concept_id
FROM (
select concept_id
from "digione".CONCEPT
where (concept_id in (4162253,36564848,4092513,4158563,4158563,4187850,4187851,4188545, 4237178,441513,44502548,4221403,4295715))
UNION
select c.concept_id
from "digione".CONCEPT c
join "digione".CONCEPT_ANCESTOR ca on c.concept_id = ca.descendant_concept_id
WHERE c.invalid_reason is null and (ca.ancestor_concept_id in (4162253,36564848,4092513,4158563,4158563,4187850,4187851,4188545,4237178,441513,44502548,4221403,4295715)) ) I
LEFT JOIN (
select concept_id from "digione".CONCEPT
where (concept_id in (4147164,139750,4162276,1075593,36712738,36712739))
UNION select c.concept_id from "digione".CONCEPT c join "digione".CONCEPT_ANCESTOR ca on
c.concept_id = ca.descendant_concept_id WHERE c.invalid_reason is null
and (ca.ancestor_concept_id in (4147164,139750,4162276,1075593,36712738,36712739)) ) E
ON I.concept_id = E.concept_id WHERE E.concept_id is null ) C;

**Additional context**
n/a

Kind regards
Birthe Lorenz