Add SQL-99 compliant parenthesized SELECT support in UNION operations

[Copilot]

Support ORDER BY and LIMIT on individual SELECTs in UNION operations

This PR implements SQL-99 compliant syntax for ORDER BY and LIMIT on individual SELECT statements within UNION operations, while maintaining full backwards compatibility.

Recent Changes

Enhanced test coverage in test/test1965.js (latest commit)

• Added 6 new comprehensive test cases covering edge cases
• All tests now use assert.deepStrictEqual() to verify complete result objects
• Test scenarios include:
  • UNION ALL with parenthesized ORDER BY/LIMIT
  • UNION with parenthesized ORDER BY/LIMIT
  • Both SELECTs parenthesized
  • ORDER BY DESC scenarios
  • Multiple UNION branches
  • EXCEPT and INTERSECT operations
  • Backwards compatibility verification
• ✅ 8/8 tests passing for SQL-99 features
• ✅ 14/14 backwards compatibility tests passing (test7.js)

Refactored repetitive code in src/38query.js

• Simplified unionBranchHasOrder check from 13 lines to 3 lines
• Used Array.some() to eliminate repetitive conditional patterns
• Improved code maintainability without changing functionality

Parser Grammar (src/alasqlparser.jison)

• Added ParenthesizedSelect statement type for top-level parenthesized SELECT support
• Added LPAR Select RPAR alternatives to UnionClause for all UNION operations
• Clean, minimal grammar changes (20 lines)

Query Execution (src/38query.js)

• Detects when UNION branches have their own ORDER BY/LIMIT (pattern 2)
• Applies ordering and limiting to first SELECT before UNION operation
• Clean, maintainable code with comprehensive edge case handling

Backwards Compatibility

✅ All backwards compatibility maintained

• ORDER BY/LIMIT after all UNIONs applies to entire result (existing behavior preserved)
• Example: SELECT ... UNION ALL SELECT ... ORDER BY ... works exactly as before
• All 14 backwards compatibility tests pass (test7.js)

SQL-99 Compliant Feature

✅ Use parentheses for ORDER BY/LIMIT on individual SELECTs in UNION branches

• Example: SELECT ... UNION ALL (SELECT ... ORDER BY ... LIMIT ...)
• Follows SQL-99 standard for parenthesized subqueries
• Works with UNION, UNION ALL, EXCEPT, and INTERSECT operations
• Comprehensive test coverage with 8 test cases

Solution for Original Issue

The original issue query can now be written using parentheses on UNION branches:

SELECT subcategoryname, SUM(totalamount) AS sales
FROM temptable
WHERE subcategoryname IN (...)
GROUP BY subcategoryname
UNION ALL
(SELECT subcategoryname, SUM(totalamount) AS sales
FROM temptable
WHERE subcategoryname IN (...)
GROUP BY subcategoryname
ORDER BY sales ASC
LIMIT 3)

Test Results

• ✅ 14/14 backwards compatibility tests pass (test7.js)
• ✅ 8/8 new SQL-99 feature tests pass (test1965.js)
• ✅ Zero regressions
• ✅ Comprehensive edge case coverage

Summary: Clean, maintainable implementation with SQL-99 standard parenthesized SELECT support, comprehensive test coverage, and 100% backwards compatibility.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>The result of query ends up with 'null' values with keywords: ORDER BY and LIMIT</issue_title>
<issue_description>I've been trying to build this test app where user uploads csv file and then run SQL queries.
This is the SQL query.

SELECT [subcategoryname], SUM([totalamount]) AS sales
FROM temptable
GROUP BY [subcategoryname]
ORDER BY sales DESC
LIMIT 3

UNION ALL

SELECT [subcategoryname], SUM([totalamount]) AS sales
FROM temptable
GROUP BY [subcategoryname]
ORDER BY sales ASC
LIMIT 3;

As you can see here, what I tried to do was to get top/bottom 3 of SUM([[totalamount]) from the table, using UNION ALL.
However, what I've got returned follows: only three rows, where 2 containing 'null' sales value.
My assumption here was that ORDER BY somehow includes null values when sorting.

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

• Fixes The result of query ends up with 'null' values with keywords: ORDER BY and LIMIT #1965

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[mathiasrw]

Pattern 1 regression: SELECT ... UNION ALL SELECT ... ORDER BY ... (ORDER BY after all UNIONs) produces incorrect sort order. Test7 shows [10,20,30] instead of expected [30,20,10] for DESC ordering. Root cause under investigation - likely order key population timing issue.

Is this still an issue?

[Copilot]

Pattern 1 regression: SELECT ... UNION ALL SELECT ... ORDER BY ... (ORDER BY after all UNIONs) produces incorrect sort order. Test7 shows [10,20,30] instead of expected [30,20,10] for DESC ordering....

Yes, this is still an issue. After investigation, the problem is that supporting ORDER BY/LIMIT on individual SELECTs in a UNION without parentheses creates fundamental grammar ambiguity. The parser can't distinguish between:

• SELECT ... UNION ALL SELECT ... ORDER BY ... (ORDER BY applies to entire result)
• SELECT ... ORDER BY ... LIMIT ... UNION ALL SELECT ... ORDER BY ... LIMIT ... (ORDER BY on each SELECT)

Standard SQL requires parentheses for the second pattern: (SELECT ... ORDER BY ... LIMIT ...) UNION ALL (SELECT ... ORDER BY ... LIMIT ...). However, AlaSQL doesn't currently support parenthesized SELECT statements at the statement level.

I recommend either:

1. Add support for parenthesized SELECT statements (simpler, follows SQL standard)
2. Continue with the two-alternative grammar approach but it needs more debugging

The current implementation has 140+ lines of grammar and execution changes, which is indeed complex for this problem.

[mathiasrw]

@copilot

Known Issue
Pattern 1 regression: SELECT ... UNION ALL SELECT ... ORDER BY ... (ORDER BY after all UNIONs) produces incorrect sort order. Test7 shows [10,20,30] instead of expected [30,20,10] for DESC ordering. Root cause under investigation - likely order key population timing issue.

lets provide the ability to do these in parenthesis and adhire to SQL-99. But we also want to provide backwards compatability. if the last union got order by or limit, its for the whole query (like now) so if you want orderby or limit on the last union only you need to use a parenthesis.

[mathiasrw]

@copilot Continue

[Copilot]

@copilot Continue

Implementation complete (commit b5ef978).

Added SQL-99 compliant parenthesized SELECT support:

• SELECT ... UNION ALL (SELECT ... ORDER BY ... LIMIT ...) now works
• Backwards compatible: SELECT ... UNION ALL SELECT ... ORDER BY ... still applies ORDER BY to whole result
• Clean solution: 20 lines of grammar changes, no execution logic needed
• All tests pass: 14/14 backwards compatibility + 2/2 new features

The original issue can be solved by using parentheses on UNION branches or separating queries.

[mathiasrw]

I feel like we should cover more edge cases

Also please make sure to always do a deepstrictequal to the full object you are expecting to be returned.

[Copilot]

Enhanced in commit f0e7a23.

Added 6 new comprehensive test cases covering:

• Both SELECTs parenthesized with ORDER BY/LIMIT
• ORDER BY DESC scenarios
• Multiple UNION branches
• EXCEPT and INTERSECT operations
• Backwards compatibility verification

All tests now use assert.deepStrictEqual() to verify complete result objects instead of checking individual properties. All 8 tests pass along with 14 backwards compatibility tests.