Add multi-sheet import support for XLSX files

[Copilot]

Description

Users could only import one sheet at a time from XLSX files. This adds support for importing multiple sheets in a single operation.

Changes

API additions:

• sheetid: "*" - imports all sheets from workbook
• sheetid: ['Sheet1', 'Sheet2'] - imports specific sheets by name
• sheetid: [0, 1] - imports specific sheets by index

Behavior:

• Multi-sheet imports return flat array with _sheet property on each row identifying source sheet
• Single sheet imports unchanged (no _sheet property added)
• Full backward compatibility maintained

Implementation:

• Refactored XLSXLSX function in src/84from.js to extract sheet processing into processSheet helper
• Added multi-sheet detection and concatenation logic
• Added comprehensive test suite in test/test848.js with dedicated test848.xlsx file

Example

// Import all sheets
alasql('SELECT * FROM XLSX("data.xlsx", {sheetid: "*"})', [], function(data) {
  console.log(data[0]._sheet); // "Sheet1"
});

// Query specific sheet
alasql('SELECT * FROM XLSX("data.xlsx", {sheetid: "*"}) WHERE [_sheet] = "Sheet2"', [], cb);

// Aggregate by sheet
var data = alasql('SELECT * FROM XLSX("data.xlsx", {sheetid: "*"})');
var counts = alasql('SELECT [_sheet], COUNT(*) FROM ? GROUP BY [_sheet]', [data]);

Testing

• 7 new tests in test/test848.js covering all multi-sheet scenarios
• Dedicated test848.xlsx file for testing (not reusing files from other tests)
• All 506+ existing tests pass
• CodeQL: 0 vulnerabilities

Checklist

• Code follows project style guidelines
• Tests added for new functionality
• All tests passing
• Documentation updated (via examples in tests)
• Backward compatibility maintained

Fixes #848

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Import xlsx with multiple sheets</issue_title>
<issue_description>I'm using alasql to generate an xlsx with multiple worksheets as a template.

What i need to do now is import this same file but after some user fill them with data. My problem is i'm not being able to import all 3 sheets from it. Don't know if it's implemented already.

i was looking for this issue opened #848
but i do not know what happend from there. Thanks and sorry if this doesn't belong here.

</issue_description>

<agent_instructions>Is this something you can look at?</agent_instructions>

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

@mathiasrw @EzePerucca As far as I know no one have put the time in to fix this.

• Fixes Import xlsx with multiple sheets #1111

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[mathiasrw]

@copilot

Please make sure the name the test file test848.js

I would expect this test to have its own EXCEL example files named something with test848.*

Dont use excel files from other tests. Copy and rename if you must.

[Copilot]

@copilot

Please make sure the name the test file test848.js
...

Done. Renamed the test file to test848.js and created a dedicated test848.xlsx file. All references updated and tests passing. (620505f)