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.

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 its local instructions, bundled resources, standard shell or editor tools, and direct verification. Show the evidence used before concluding."
• Do not claim an MCP operation was used when the active host does not expose it.
• Treat local files, tests, rendered outputs, logs, or screenshots as the fallback evidence path.

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

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.