Add union all clause

[jhchabran]

No description provided.

[codecov-commenter]

Codecov Report

Merging #408 (fdea749) into main (8812a7a) will increase coverage by 0.20%.
The diff coverage is 48.27%.

@@            Coverage Diff             @@
##             main     #408      +/-   ##
==========================================
+ Coverage   68.15%   68.36%   +0.20%     
==========================================
  Files          82       83       +1     
  Lines        7760     7789      +29     
==========================================
+ Hits         5289     5325      +36     
+ Misses       1809     1792      -17     
- Partials      662      672      +10     

Impacted Files	Coverage Δ
internal/query/statement/select.go	87.34% <0.00%> (-2.27%)	⬇️
internal/sql/scanner/token.go	10.71% <ø> (ø)
internal/sql/parser/select.go	57.83% <50.00%> (-1.33%)	⬇️
internal/stream/concat.go	50.00% <50.00%> (ø)
internal/planner/optimizer.go	75.82% <55.55%> (+0.61%)	⬆️
internal/query/query.go	52.87% <0.00%> (+20.68%)	⬆️

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