Imported from practicalswan/agent-skills (sql-development/SKILL.md). Install upstream with npx skills add practicalswan/agent-skills --skill sql-development. Copyright stays with the author.

SQL Development

Optimized for current PostgreSQL, MySQL, and SQL Server releases plus migration-first database workflows.

Comprehensive SQL development guidelines combining SQL coding standards, stored procedure generation, and MS SQL Server DBA best practices.

• Leverage native parallel subagent dispatch and 200k+ context windows where available.

Anti-Patterns

• Using SELECT * in production queries: It hides contract drift and pulls more data than the caller needs.
• Writing non-SARGable predicates: Functions on indexed columns turn otherwise cheap queries into table scans.
• Ignoring transaction and lock behavior: Correct SQL needs both logical correctness and concurrency safety.

Verification Protocol

Before claiming "skill applied successfully":

1. Pass/fail: The SQL Development implementation names the target runtime, framework version, and affected files.
2. Pass/fail: Build, lint, test, or equivalent local validation is run for the changed surface.
3. Pass/fail: Edge cases for errors, dependency drift, and environment differences are addressed or explicitly out of scope.
4. Pressure-test scenario: Apply the workflow to a change that passes happy-path tests but fails one boundary condition.
5. Success metric: Zero untested success claims; every implementation claim maps to a command or artifact.

Before and After Example

-- Before
SELECT *
FROM Orders
WHERE YEAR(created_at) = 2026;

-- After
SELECT order_id, customer_id, created_at, total_amount
FROM Orders
WHERE created_at >= '2026-01-01'
  AND created_at < '2027-01-01';

Uses explicit columns and a SARGable date range so indexes can do their work.

Activation Conditions

Use symptom -> action triggers: when one matches, apply this skill and verify with the protocol below.

• Writing SQL queries and stored procedures
• Designing database schemas and table structures
• Working with MS SQL Server as a DBA
• Performance tuning and query optimization
• Database backup, restore, and security configuration
• SQL Server 2025+ feature adoption and migration

Part 1: Database Schema Design

Table Naming

• All table names in singular form
• All column names in singular form

Required Columns

• All tables must have a primary key column named id
• All tables must have created_at for creation timestamp
• All tables must have updated_at for last update timestamp

Constraints

• All tables must have a primary key constraint
• All foreign key constraints must have a name
• All foreign key constraints defined inline
• All foreign keys must have ON DELETE CASCADE
• All foreign keys must have ON UPDATE CASCADE
• All foreign keys must reference the primary key of the parent table

Part 2: SQL Coding Style

Formatting

• Uppercase for SQL keywords (SELECT, FROM, WHERE)
• Consistent indentation for nested queries
• Comments to explain complex logic
• Break long queries into multiple lines
• Organize clauses: SELECT, FROM, JOIN, WHERE, GROUP BY, HAVING, ORDER BY

Query Structure

• Use explicit column names, never SELECT *
• Qualify column names with table alias when using multiple tables
• Prefer JOINs over subqueries when possible
• Include LIMIT/TOP clauses to restrict result sets
• Use appropriate indexing for frequently queried columns
• Avoid functions on indexed columns in WHERE clauses

Part 3: Stored Procedure Standards

Naming Conventions

• Prefix with usp_
• Use PascalCase: usp_GetCustomerOrders
• Include plural noun for multiple records: usp_GetProducts
• Include singular noun for single record: usp_GetProduct

Parameter Handling

• Prefix parameters with @
• Use camelCase: @customerId
• Provide default values for optional parameters
• Validate parameter values before use
• Document parameters with comments
• Required parameters first, optional later

Structure

• Include header comment block with description, parameters, return values
• Return standardized error codes/messages
• Return result sets with consistent column order
• Use OUTPUT parameters for returning status information
• Prefix temporary tables with tmp_
• Include SET NOCOUNT ON for data-modifying procedures

Part 4: Security Best Practices

Query Security

• Parameterize all queries to prevent SQL injection
• Use prepared statements for dynamic SQL
• Avoid embedding credentials in SQL scripts
• Proper error handling without exposing system details
• Avoid dynamic SQL in stored procedures

Transaction Management

• Explicitly begin and commit transactions
• Use appropriate isolation levels
• Avoid long-running transactions that lock tables
• Use batch processing for large data operations

Part 5: MS SQL Server DBA

Tooling

• Install and enable ms-mssql.mssql VS Code extension for full database management
• Use official Microsoft documentation for reference and troubleshooting

DBA Responsibilities

• Database creation and configuration
• Backup and restore strategies
• Performance tuning and index optimization
• Security management and auditing
• Upgrades and compatibility planning (SQL Server 2025+)

Best Practices

• Focus on tool-based database inspection over codebase analysis
• Highlight deprecated/discontinued features in SQL Server 2025+
• Encourage secure, auditable, performance-oriented solutions
• Reference official docs for troubleshooting
• Warn about deprecated features and suggest alternatives

Troubleshooting

Common Pitfalls

• Using SELECT * in production queries: It hides contract drift and pulls more data than the caller actually needs.
• Writing non-SARGable predicates: Functions on indexed columns turn otherwise cheap queries into table scans.
• Skipping transaction and lock analysis: Correct SQL needs both logical correctness and concurrency safety.

References & Resources

Documentation

• T-SQL Patterns — MERGE, CTEs, PIVOT, JSON operations, window functions, and error handling
• Performance Tuning — Execution plans, index tuning, Query Store, and anti-patterns

Scripts

• Stored Procedure Template — Production-ready SP template with TRY/CATCH, pagination, and dynamic sorting

Examples

• Schema Design Example — Recipe Management System with 10 tables, stored procedures, and migrations

Cross-Client Portability

This skill is written to stay usable across GitHub Copilot, Claude Code, and Codex.

• GitHub Copilot: keep the folder in a Copilot-visible skill path or wrap the workflow in project instructions when folder discovery is unavailable.
• Claude Code: keep the folder in a local skills directory or a compatible plugin source.
• Codex: install or sync the folder into $CODEX_HOME/skills/sql-development and restart Codex after major changes.

MCP Availability And Fallback

Preferred MCP Server: None required

• Fallback prompt: "Use the SQL Development skill without MCP. Rely on the local SKILL.md, bundled references or scripts, and manual verification. Show the exact commands, evidence, and final checks you used before concluding."
• If the current host does not expose a matching server, use the bundled references, scripts, native toolchain, and manual workflow already described in this skill.
• Treat direct local verification, rendered output, logs, tests, or screenshots as the fallback evidence path before completion.

Related Skills

• php-development: Use it when the workflow also needs modern PHP backend implementation.
• powerbi-modeling: Use it when the workflow also needs Power BI semantic model design and DAX work.
• code-quality: Use it when the workflow also needs two-stage review (spec compliance first, then code quality), maintainability, and refactoring guidance.
• systematic-debugging: Use it when the workflow also needs root-cause debugging before proposing fixes.