---

📊 Headline result

Fine-tuning a 1.5B model with a single LoRA adapter lifted execution accuracy by +8.1 points on the full Spider dev set — and cut the number of crashing queries by 35%.

	Execution accuracy	Correct (of 1034)	Crashing queries
Base Qwen2.5-Coder-1.5B (zero-shot)	57.45%	594	228
+ QLoRA fine-tune (SQLForge)	65.57%	678	148
	+8.12 pts	+84	−80 (−35%)

Measured on the full 1034-example Spider validation split, by running every generated query against the real SQLite database and comparing result sets. Trained on a single RTX 3070 (8GB). See the runs on W&B →

---

What this is

A from-scratch fine-tuning project, not an API wrapper. It takes a small open code model, teaches it text-to-SQL with QLoRA, and proves the improvement with a proper execution-accuracy harness on Spider.

The goal is to demonstrate the full ML loop — data → train → evaluate → serve → ship — with experiment tracking, an honest before/after, error analysis, and an interactive demo that runs the generated SQL against live databases.

Why execution accuracy (and why it matters)

Most text-to-SQL demos compare the predicted query string to the gold string. That's fragile — two very different queries can be equally correct, and two near-identical strings can differ by one wrong column.

SQLForge instead runs each generated query against the actual SQLite database and compares the result sets (order-insensitive unless the gold query uses ORDER BY). If the gold query itself fails, the example is skipped rather than counted. This is the same metric used by the Spider execution-accuracy leaderboard, and it's the honest one.

The agentic twist: self-correction

When a generated query crashes (e.g. no such column), SQLForge doesn't just mark it wrong — it feeds the SQL and the database error back to the model, hands it the exact valid table/column names, and lets it retry. You can watch this happen live in the demo's self-correction trace.

Honest note: self-correction recovers some crashes but only nudges overall accuracy by ~1 point — a 1.5B model often repeats its own mistake. It's a genuinely useful, transparent feature, and an honest illustration of a small model's reasoning ceiling. See Limitations.

Architecture

flowchart LR
    A[Spider<br/>question + schema] --> B[Qwen2.5-Coder-1.5B<br/>4-bit + QLoRA adapter]
    B --> C[generated SQL]
    C --> D{run on<br/>real SQLite DB}
    D -- error --> E[self-correction:<br/>feed error + valid names back]
    E --> B
    D -- rows --> F[compare result sets<br/>= execution accuracy]

Live demo

A FastAPI server + a custom dark UI: pick a database, ask a question, and watch the model write the SQL, run it, and show the results — with the self-correction trace when it retries.

• 🤗 Hosted: huggingface.co/spaces/Abdullahkousa2/sqlforge
• 💻 Local:

  python -m uvicorn app.server:app --port 8000
  # then open http://localhost:8000
  

Install (library)

pip install sqlforge

Use the inference + evaluation toolkit directly:

from sqlforge.inference import load_model, generate_sql

model, tok = load_model("Qwen/Qwen2.5-Coder-1.5B-Instruct",
                        adapter_path="Abdullahkousa2/sqlforge-qwen2.5-coder-1.5b")

schema = '''CREATE TABLE singer ("Singer_ID" int, "Name" text, "Age" int);'''
print(generate_sql(model, tok, schema, "How many singers are there?"))
# -> SELECT count(*) FROM singer

Or from the command line:

sqlforge --db mydata.sqlite --question "How many users signed up after 2020?"

Reproduce the pipeline

The whole thing runs on a single 8GB GPU. Steps are also available as a guided notebook: run_pipeline.ipynb.

# 0. install (torch is assumed pre-installed; see requirements.txt)
pip install -r requirements.txt

# 1. data
python scripts/download_data.py        # Spider question/SQL pairs (HF)
python scripts/download_databases.py   # Spider SQLite databases
python scripts/prepare_data.py         # -> data/processed/{train,validation}.jsonl

# 2. baseline (the "before" number)
python scripts/evaluate.py --no-4bit --wandb

# 3. fine-tune (QLoRA, ~3 epochs on an RTX 3070)
python scripts/train.py

# 4. fine-tuned eval (the "after" number)
python scripts/evaluate.py --adapter outputs/qwen2.5-coder-1.5b-sql --no-4bit --wandb

# 5. self-correction eval
python scripts/evaluate.py --adapter outputs/qwen2.5-coder-1.5b-sql --no-4bit --self-correct --wandb

Training configuration

Base model	Qwen/Qwen2.5-Coder-1.5B-Instruct
Method	QLoRA — 4-bit NF4 base + LoRA adapter
LoRA	r=16, α=32, dropout=0.05, all attention + MLP projections
Schedule	3 epochs, lr 2e-4 cosine, warmup 0.03
Batching	per-device 1 × grad-accum 16 (effective 16)
Memory	gradient checkpointing, paged AdamW 8-bit, bf16
Seq length	1280 (the ~3% longer examples are dropped, never truncated)

Full config: configs/train_config.yaml.

Repository layout

sqlforge/            # the library: prompt format, inference, execution-accuracy grader
  prompts.py         #   single source of truth for the prompt (no train/eval skew)
  inference.py       #   model loading, generation, self-correction loop
  exec_eval.py       #   run SQL on SQLite, compare result sets
scripts/             # download → prepare → train → evaluate
app/                 # FastAPI demo server + custom dark UI (static/)
configs/             # training config
run_pipeline.ipynb   # the whole pipeline as a guided notebook

Limitations

Stated plainly, because honest evaluation is the point:

• The model is small (1.5B). Its dominant failure is over-joining — building an unnecessary JOIN and referencing a column on the wrong table (no such column). Fine-tuning reduced this by a third but couldn't eliminate it.
• ~90% needs a different class of system. Top of the Spider leaderboard means a frontier model (GPT-4 / Claude) inside an agentic pipeline (DIN-SQL / DAIL-SQL: schema linking, decomposition, self-consistency). A locally-trained 1.5B realistically tops out in the 60s–70s.
• A 200-example eval is noise. An early 200-sample read showed 49.5%→51.5%; the full 1034-example set revealed the true 57.4%→65.6%. Always evaluate the full split.

Roadmap

• Scale to a 3B/7B base for the mid-70s
• Stop-string decoding to speed up worst-case generation
• BIRD dataset augmentation
• Schema-linking pre-step before generation

Tech stack

PyTorch · 🤗 Transformers · PEFT · TRL · bitsandbytes · Datasets · Weights & Biases · FastAPI

License

MIT © Abdullah Kousa