[release/7.0] Fix to #30575 - Multiple LeftJoins (GroupJoins) lead to GroupJoin Exception when the same where is used twice #30794
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Ported from #30594
Fixes #30575
Description
Query with more multiple GroupJoin-SelectMany-DefaultIfEmpty (i.e. LEFT JOIN pattern), which use a variable, produces incorrect query.
Customer impact
Query with more multiple GroupJoin-SelectMany-DefaultIfEmpty (i.e. LEFT JOIN pattern), which use a variable, produces incorrect query. Workaround is to not use variable (i.e. constant) which is easy, when possible, but often not realistic.
How found
Customer report on 7.0.
Regression
No.
Testing
Added regression tests.
Risk
Minimal; Fix is very simple (1 line change) - an improved way to identify lambda arguments vs user variables (by looking at the name prefix). We use this strategy in other places in the code base already, so the approach has been thoroughly tested. As always, added quirk just in case.