SQLGraph subgraph query improvements and minor fixes

[JoOkuma]

No description provided.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.89%. Comparing base (35996ee) to head (c757266).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #97      +/-   ##
==========================================
+ Coverage   88.83%   88.89%   +0.05%     
==========================================
  Files          42       42              
  Lines        2258     2270      +12     
  Branches      389      388       -1     
==========================================
+ Hits         2006     2018      +12     
  Misses        153      153              
  Partials       99       99              

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