Implementation of EXISTS and NOT EXISTS

[joka921]

This implements EXISTS via a new ExistsJoin operation. Namely, for each operation involving an expression (for example, a BIND or a FILTER), an ExistJoin operation is added for each occurence of EXISTS in that expression. The ExistsJoin adds an additional column (with a unique variable name) that contains the result of the EXISTS and is used to evaluate the expression. This can can be seen in the "Analysis" tree when executing a query. The current implementation has the following limitations, which will be addressed in future PRs:

1. The ExistsJoin operation is not yet lazy
2. The argument of an EXISTS is currently handled completely independent from the rest of the query (except for FROM AND FROM NAMED clauses, which are inherited from the outer query); it is an ongoing debate whether that is correct when the EXISTS contains FILTERs that refer to variables from outside the EXISTS.
3. When there are UNDEF values in the join columns, the ExistsJoin uses our generic zipper join, which is not particularly efficient

[codecov]

Codecov Report

Attention: Patch coverage is 92.76018% with 16 lines in your changes missing coverage. Please review.

Project coverage is 90.12%. Comparing base (6349abd) to head (092e0d9).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/engine/MultiColumnJoin.cpp	14.28%	4 Missing and 2 partials ⚠️
src/util/JoinAlgorithms/FindUndefRanges.h	77.27%	0 Missing and 5 partials ⚠️
src/engine/ExistsJoin.cpp	96.36%	2 Missing and 2 partials ⚠️
src/engine/ExistsJoin.h	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1703      +/-   ##
==========================================
+ Coverage   90.07%   90.12%   +0.04%     
==========================================
  Files         396      399       +3     
  Lines       38021    38199     +178     
  Branches     4266     4281      +15     
==========================================
+ Hits        34247    34426     +179     
+ Misses       2486     2473      -13     
- Partials     1288     1300      +12     

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[hannahbast]

This looks great and I have made a thorough pass now and committed some changes. A few more questions and then this is ready to merge:

1. In the code for ExistsExpression::getCacheKey you mention that it can happen that the ExistsJoin is not yet set up because the query planning is not yet finished, in which case you set a random cache key. For which scenario is this relevant? In particular, when does it ever happen that query processing starts before query planning is completed?

2. In SparqlAntlrParserTest.cpp, you define a selectABarFooMatcher, which can take FROM and FROM NAMED clauses as arguments. But then you only use it with the default arguments.

3. At the end of ExistsJoinTest.cpp there are two TODOs by yourself suggesting a few more tests, how about adding them?

4. Is it hard to use ad_utility::callFixedSize for the ExistsJoin or should that be a separate PR?

5. Can you check the one SonarCloud issue that is not a TODO?

6. Are you fine with the patch coverage reported by CodeCov?

[hannahbast]

@joka921 This looks great now, thanks a lot. I tried it on a few queries on Wikidata and they worked fine. I have committed some minor comment improvements and then this should be almost ready to merge, provided that all the tests run through.

What I don't understand is the addition of https://github.com/ad-freiburg/qlever/blob/87ba7cad5b1124b4095beb9fa31b040e85a7de17/.github/workflows/upload-sparql-conformance.yml . In the current master, we have https://github.com/ad-freiburg/qlever/blob/master/.github/workflows/sparql-conformance-uploader.yml, which looks a bit different though. Please clarify.

[sparql-conformance]

Conformance check passed ✅

Test Status Changes 📊

Number of Tests	Previous Status	Current Status
15	Failed	Passed

Details: https://qlever.cs.uni-freiburg.de/sparql-conformance-ui?cur=092e0d91d22d3e541253dfcce728fd6cd5d5065e&prev=6349abdcf85d66c231dd4527c987d05b21177cf7

[sonarqubecloud]

Quality Gate passed

Issues
4 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[hannahbast]

I reverted the involuntary changes in .github/workflows (regarding the SPARQL conformance test) and fixed another small merge bug. Everything looks great and I will happily merge this now!

PS: The failing macOS check has nothing to do with this PR in particular (the packet installation step fails).