[WIP] Fix joinstar option not working in alasql

[Copilot]

• Investigate and understand the issue with joinstar option
• Create test case (test547.js) to reproduce the issue
• Analyze the code to find where the issue occurs
• Fix the issue in the select compilation code
• Verify the fix with tests
• Run full test suite to ensure no regressions

Original prompt

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This section details on the original issue you should resolve

<issue_title>joinstar option not working</issue_title>
<issue_description>Spawned from #547 (comment)

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The alasql.options.joinstar option seems not working now.

If we reproduce the example of @filipkis, but defining alasql.options.joinstar = 'underscore', the result is not the expected:

var data = [{ dep: 'A', qt: 10, price: 5, extra: 1}];
var data2 = [{ dep: 'B', qt: 2, price: 5}];
alasql.options.joinstar = 'underscore';	 
var res = alasql('SELECT * FROM ? as a JOIN ? as b',[data,data2]);

results is:

[{"dep":"B","qt":2,"price":5,"extra":1}]

and it should be

[{ data_dep: 'A', data_qt: 10, data_price: 5, data_extra: 1,data2_dep: 'B', data2_qt: 2, data2_price: 5 }]

if I'm not wrong.
</issue_description>

<agent_instructions>Im not sure this is still a problem. Please investigate. </agent_instructions>

Comments on the Issue (you are @copilot in this section)

@mathiasrw Thank you so much for looking into this :) @mathiasrw Not that I know of. Any inputs or PR's would be greatly appreciated.

• Fixes joinstar option not working #1004

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[mathiasrw]

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