Correct Handling of UNION Queries with Literals in the Vitess Planner

[systay]

Description

The Vitess planner was previously unable to handle UNION queries that included literals, resulting in an error. For example, the following query:

select 'a' as type, 0 as id from user group by 2 
union all 
select 'c' as type, 0 as id from user_extra as t

Results in:

VT12001: unsupported: argument offsets did not line up for UNION

Solution:

To address this issue, the solution ensures that all operators that truncate columns actually perform the truncation during the planning phase. This alignment guarantees that the argument offsets match correctly for UNION queries, preventing the aforementioned error.

Related Issue(s)

Fixes #16228

Checklist

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Deployment Notes

[vitess-bot]

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[codecov]

Codecov Report

Attention: Patch coverage is 88.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 68.61%. Comparing base (f118ba2) to head (3039c4e).
Report is 201 commits behind head on main.

❗ Current head 3039c4e differs from pull request most recent head 826abd6

Please upload reports for the commit 826abd6 to get more accurate results.

Files	Patch %	Lines
go/vt/vtgate/planbuilder/operators/aggregator.go	81.25%	3 Missing ⚠️
go/vt/vtgate/planbuilder/operators/union.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16227      +/-   ##
==========================================
+ Coverage   68.40%   68.61%   +0.20%     
==========================================
  Files        1556     1544      -12     
  Lines      195121   197992    +2871     
==========================================
+ Hits       133479   135844    +2365     
- Misses      61642    62148     +506     

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[frouioui]

Looks good to me. Should we merge this to release-20.0/-rc since it's a bug fix?

[harshit-gangal]

Earlier, we wanted the truncation to happen only at the topmost operator that supported truncation. With the current changes, is there a case where the truncation is done by multiple operators?