Add regression test for GROUP BY with no matching rows

[Copilot]

Description

The issue reported that SELECT Name FROM ? WHERE 1=0 GROUP BY Name was returning [{Name: 'undefined'}] instead of an empty result set. This behavior has already been fixed in the codebase.

The fix exists in src/38query.js:102 where the condition if (query.groups.length === 0 && query.allgroups.length === 0) ensures artificial groups are only created when no GROUP BY clause exists. This correctly implements SQL standard behavior:

• GROUP BY with no matches → []
• Aggregates without GROUP BY with no matches → one row with defaults (e.g., [{cnt: 0}])

Changes

Added comprehensive test suite in test/test79-B.js covering:

• GROUP BY returning empty results when WHERE matches no rows
• GROUP BY with aggregates on empty result sets
• GROUP BY on empty datasets
• Multi-column GROUP BY with no matches
• Aggregates without GROUP BY correctly returning default values
• Verification that GROUP BY works correctly with matching data

Example

// Returns [] as expected
alasql('SELECT Name FROM ? WHERE 1=0 GROUP BY Name', [[{Name: 'test'}]]);

// Returns [{cnt: 0}] as expected (aggregate without GROUP BY)
alasql('SELECT COUNT(*) as cnt FROM ? WHERE 1=0', [[{Name: 'test'}]]);

[!WARNING]

Original prompt

---

This section details on the original issue you should resolve

<filter_complete></filter_complete>

<issue_title>GROUP BY returns 1 invalid result if no rows meet condition </issue_title>
<issue_description>If there is a query that has no results, but contains a GROUP BY, it returns one result regardless, with the data of "undefined"

console.log(alasql('SELECT Name FROM ? WHERE 1=0 GROUP BY Name',[[{Name:'test'}]]));
returns: [{Name: 'undefined'}] but should be []

</issue_description>

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

@agershun Thank you! For the second question you should: a) add Name to the GROUP BY clause b) Use FIRST() aggregator

var res = alasql('SELECT Type,Name FROM ? GROUP BY Type, Name',[...);

or

var res = alasql('SELECT Type,FIRST(Name) FROM ? GROUP BY Type',[...]);

For the first question - sorry, it still in progress...
</comment_new>
<comment_new>@agershun
Try this example in jsFiddle
</comment_new>
<comment_new>@mathiasrw
👍
</comment_new>
<comment_new>@agershun
Is there a way you can test if the fields are requested naked, to automatically apply the FROM() function when used in a GROUP BY?

I think, that the standard SQL reaction is to throw a error like "column is not found". I think, Alasql can check this, but only for SELECT with GROUP BY clause. Plus, it is hard to recognize these "naked" columns in expressions, like:

    SELECT mycol+1 FROM mytable GROUP BY othercol

</comment_new>
<comment_new>@mathiasrw
Is this issue resolved?
</comment_new>
<comment_new>@mathiasrw
Well... its now returning [{}] instead of the original problem - but its still not correct.

Any help to resolve this would be awesome.

http://jsfiddle.net/t780pnz1/</comment_new>

• Fixes GROUP BY returns 1 invalid result if no rows meet condition  #79

Original prompt

---

This section details on the original issue you should resolve

<issue_title>GROUP BY returns 1 invalid result if no rows meet condition </issue_title>
<issue_description>If there is a query that has no results, but contains a GROUP BY, it returns one result regardless, with the data of "undefined"

console.log(alasql('SELECT Name FROM ? WHERE 1=0 GROUP BY Name',[[{Name:'test'}]]));
returns: [{Name: 'undefined'}] but should be []

</issue_description>

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

@agershun Thank you! For the second question you should: a) add Name to the GROUP BY clause b) Use FIRST() aggregator

var res = alasql('SELECT Type,Name FROM ? GROUP BY Type, Name',[...);

or

var res = alasql('SELECT Type,FIRST(Name) FROM ? GROUP BY Type',[...]);

For the first question - sorry, it still in progress...

@agershun Try this example [in jsFiddle](http://jsfiddle.net/trr2b7qv/2/) @mathiasrw 👍 @agershun **Is there a way you can test if the fields are requested naked, to automatically apply the FROM() function when used in a GROUP BY?**

I think, that the standard SQL reaction is to throw a error like "column is not found". I think, Alasql can check this, but only for SELECT with GROUP BY clause. Plus, it is hard to recognize these "naked" columns in expressions, like:

    SELECT mycol+1 FROM mytable GROUP BY othercol

@mathiasrw Is this issue resolved? @mathiasrw Well... its now returning `[{}]` instead of the original problem - but its still not correct.

Any help to resolve this would be awesome.

http://jsfiddle.net/t780pnz1/</comment_new>

• Fixes GROUP BY returns 1 invalid result if no rows meet condition  #79

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[mathiasrw]

@copilot Continue

[Copilot]

@copilot Continue

Renamed test file from test/test926.js to test/test79-B.js and updated the test description. All tests pass. (6626dca)