CharlesKWON
6c8d5f8b3b
A scalar correlated subquery with a JOIN inside:
SELECT e.name,
(SELECT SUM(o.qty * p.price)
FROM ord o INNER JOIN prod p ON o.prod_id = p.id
WHERE o.emp_id = e.id) AS revenue
FROM emp e WHERE e.dept = 'SALES'
returned wrong values (equal to SUM(qty) instead of SUM(qty*price))
or zero for all but the first outer row. Root cause was a triple
interaction between three independent bugs.
--- Bug 1: Subquery cache leaked across five_SQL invocations ---
hSubCorrCache, aSubCacheSlots, aSemiJoinSlots, nSubCacheSeq were
declared as DATA ... INIT { => } / {} / 0. In Five's compiled output,
hash/array INIT literals may share the same backing instance across
New() calls, so the cache from query A (SUM qty, no join) was still
there when query B ran, providing a hit on the same key — returning
A's cached (wrong) value instead of re-executing B's subquery.
Fix: explicit initialization in New().
--- Bug 2: aJoins alias mutation across subquery invocations ---
RunSelect's join-alias sync loop mutated aJoins[i][3] from the
user alias ("p") to the depth-suffixed temp alias ("FA_0003").
aJoins was a direct reference into hQuery["joins"], so the mutation
persisted across re-executions of the same hQuery. On the 2nd call,
the sync loop couldn't find a matching aTables entry because the
stale temp alias ("FA_0003") didn't match the new one ("FA_0005").
The join table's workarea was positioned wrong → empty join result.
Fix: deep-clone both ::aTables and aJoins at the start of RunSelect
so each invocation starts from the parsed originals.
--- Bug 3: SqlCollectCols stripped alias prefixes ---
When adding hidden columns for complex aggregate arguments (e.g.
SUM(o.qty * p.price)), SqlCollectCols returned bare names like
"qty" and "price" instead of qualified "o.qty" / "p.price". In a
JOIN context, unqualified "price" routed FetchRow to the first
table (ord) instead of prod — FieldPos returned 0, the column was
silently NIL, and the multiplication collapsed to qty*1 = qty.
Fix: new SqlCollectColExprs returns the original ND_COL AST nodes
with qualified names preserved. The hidden-column loop now inserts
these directly so FetchRow's dot-qualified path resolves to the
correct workarea via FindWA.
--- Verification ---
Deterministic 5-emp / 6-order / 3-product test:
Expected revenues per emp:
Emp 1: 2*10 + 3*20 = 80 → got 80.00 ✓
Emp 2: 1*10 + 4*30 = 130 → got 130.00 ✓
Emp 3: 5*20 = 100 → got 100.00 ✓
Emp 4: no orders = 0 → got 0 ✓
Emp 5: 7*10 = 70 → got 70.00 ✓
Also verified SUM(qty*2) and SUM(p.price) variants.
Validation:
- FiveSql2 43/43
- Harbour compat 51/51
- go test ./... ALL PASS
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
FiveSql2 — SQL Engine for Harbour DBF/NTX/CDX
Pratt parser + SQL:1992-2023 full standard support Supports both NTX (Clipper) and CDX (FoxPro/ADS) indexes
Architecture
five_SQL("SELECT ...")
│
├── TSqlLexer Tokenizer
├── TSqlParser2 Pratt parser (data-driven operators)
├── TSqlExecutor Query executor (Volcano model)
│ ├── TSqlAlias Central alias manager (no collisions)
│ ├── TSqlIndex NTX/CDX index optimization (auto-detect)
│ ├── TSqlAgg GROUP BY / aggregation
│ ├── TSqlSort ORDER BY / DISTINCT
│ ├── TSqlDDL CREATE/DROP/ALTER TABLE/INDEX
│ └── TSqlTxn BEGIN/COMMIT/ROLLBACK
├── TSqlExpr AST nodes + expression evaluation
└── TSqlFunc 60+ scalar functions
Build & Test
export PATH="/path/to/harbour-core/bin/linux/gcc:$PATH"
export HB_INSTALL_PREFIX="/path/to/harbour-core"
make # Build all tests
make test # Run all 157 tests
make bench # Parser benchmark
make clean # Clean
SQL Standard Coverage
| Standard | Features | Tests |
|---|---|---|
| SQL:1992 | SELECT, JOIN, GROUP BY, HAVING, Subquery, CASE, CAST | 43 |
| SQL:1999 | CTE, Recursive CTE, Window Functions, MERGE | 10 |
| SQL:2003 | SIMILAR TO, GROUPING SETS, LATERAL, Window frames | 64 |
| SQL:2008 | FETCH/OFFSET, FOR UPDATE, Extended MERGE | (incl.) |
| SQL:2016 | JSON functions, LISTAGG | (incl.) |
| SQL:2023 | ANY_VALUE, GREATEST/LEAST, BOOL_AND/OR | (incl.) |
| Challenge | LeetCode-level complex queries | 15 |
| Extreme | Production analytics stress tests | 15 |
Adding New Operators
Edit TSqlParser2.prg, method InitInfixTables():
::hInfixTT[ TK_MYOP ] := { "<=>", 40, 41, ND_BIN }
One line. No structural changes needed.
Copyright
Copyright (c) 2025-2026 Charles KWON (Charles KWON OhJun) Email: charleskwonohjun@gmail.com All rights reserved.