SQL Database Assistant

Category: Engineering Domain: Database Development & Optimization

Overview

The SQL Database Assistant skill provides tools for analyzing SQL query performance, exploring database schemas from DDL files, and generating migration SQL from schema differences. It helps teams write efficient queries, maintain clean schemas, and manage database evolution safely.

Clarify First

Before analyzing or generating, confirm these inputs. If any is unknown or vague, ASK — do not assume:

• Task — query optimization / schema documentation / migration generation (selects the script)
• SQL input — the query, the DDL file, or the from/to schema pair to operate on (the script's actual input)
• Target database / dialect — Postgres / MySQL / etc. (changes index recommendations and migration SQL syntax)

Stop rule: ask only the 2-3 that most change the output. If the user says "just draft it," proceed and list your assumptions at the top of the artifact.

Quick Start

# Analyze a SQL query for performance issues
python scripts/query_optimizer.py --file slow_query.sql

# Analyze inline SQL
python scripts/query_optimizer.py --query "SELECT * FROM users WHERE name LIKE '%john%'"

# Explore schema from DDL file
python scripts/schema_explorer.py --file schema.sql

# Generate migration from schema diff
python scripts/migration_generator.py --from old_schema.sql --to new_schema.sql

# JSON output
python scripts/query_optimizer.py --file query.sql --format json

Tools Overview

query_optimizer.py

Analyzes SQL queries for performance issues and optimization opportunities.

Feature	Description
SELECT * detection	Flags queries selecting all columns
Missing index hints	Identifies WHERE/JOIN columns likely needing indexes
N+1 detection	Flags correlated subquery patterns
Full table scan	Detects queries without WHERE clauses on large tables
JOIN analysis	Checks join conditions and types
LIKE optimization	Flags leading wildcard LIKE patterns

schema_explorer.py

Generates documentation from SQL DDL (CREATE TABLE) files.

Feature	Description
Table catalog	Lists all tables with column counts
Column details	Documents types, nullability, defaults
Index listing	Catalogs indexes and their columns
Relationship mapping	Identifies foreign key relationships
Markdown output	Generates schema documentation

migration_generator.py

Generates migration SQL by comparing two schema DDL files.

Feature	Description
Column additions	ALTER TABLE ADD COLUMN for new columns
Column removals	ALTER TABLE DROP COLUMN for removed columns
Type changes	ALTER TABLE ALTER COLUMN for type modifications
New tables	CREATE TABLE for entirely new tables
Dropped tables	DROP TABLE for removed tables
Index changes	CREATE/DROP INDEX for index differences

Workflows

Query Optimization Workflow

1. Identify slow queries - Collect queries from slow query log
2. Analyze - Run query_optimizer.py on each query
3. Review findings - Prioritize by estimated impact
4. Optimize - Apply suggested improvements
5. Verify - Re-analyze to confirm optimization

Schema Documentation Workflow

1. Export DDL - Dump schema from database
2. Explore - Run schema_explorer.py to generate docs
3. Review - Check relationships and data types
4. Publish - Include in project documentation

Migration Workflow

1. Capture current - Export current schema DDL
2. Define target - Write desired schema DDL
3. Generate migration - Run migration_generator.py
4. Review SQL - Check generated migration for safety
5. Test - Apply to staging database first
6. Deploy - Apply to production with rollback plan

CI Integration

# Lint SQL queries
python scripts/query_optimizer.py --file queries/ --format json --strict

# Generate schema docs
python scripts/schema_explorer.py --file schema.sql --format markdown > SCHEMA.md

Reference Documentation

• SQL Optimization - Index strategies, query patterns, anti-patterns

Common Patterns Quick Reference

Query Anti-Patterns

Pattern	Issue	Fix
SELECT *	Fetches unnecessary data	List specific columns
LIKE '%term%'	Cannot use index	Use full-text search
Correlated subquery	N+1 query pattern	Rewrite as JOIN
No WHERE clause	Full table scan	Add filtering conditions
OR in WHERE	Poor index usage	Use UNION or IN
Functions on indexed columns	Prevents index use	Apply to value side

Index Guidelines

Query Pattern	Index Type
WHERE col = value	B-tree on col
WHERE col1 = v AND col2 = v	Composite (col1, col2)
ORDER BY col	B-tree on col
WHERE col LIKE 'prefix%'	B-tree on col
WHERE col IN (...)	B-tree on col
Full-text search	Full-text index

Migration Safety

• Always generate rollback SQL alongside forward migration
• Test migrations against a copy of production data
• Add columns as nullable first, then backfill, then add constraints
• Never rename columns directly; add new, migrate data, drop old