Agent-Skills.md

Agent Skills: SQL Expert

Expert SQL query writing, optimization, and database schema design with support for PostgreSQL, MySQL, SQLite, and SQL Server. Use when working with databases for: (1) Writing complex SQL queries with joins, subqueries, and window functions, (2) Optimizing slow queries and analyzing execution plans, (3) Designing database schemas with proper normalization, (4) Creating indexes and improving query performance, (5) Writing migrations and handling schema changes, (6) Debugging SQL errors and query issues

UncategorizedID: aiskillstore/marketplace/sql-expert

Repository

aiskillstore/marketplace
aiskillstore
23014

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pnpm dlx add-skill https://github.com/aiskillstore/marketplace/tree/HEAD/skills/hmohamed01/sql-expert

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skills/hmohamed01/sql-expert/SKILL.md

Skill Metadata

Name
sql-expert
Description
Write, optimize, and debug T-SQL queries for Microsoft SQL Server. Covers CTEs, window functions, PIVOT, MERGE, APPLY operators, execution plan analysis, indexing strategies, and stored procedures. Use when working with SQL Server, T-SQL scripts, .sql files, stored procedures, query optimization, or database performance tuning.

SQL Expert

Expert assistance for Microsoft SQL Server and T-SQL development.

Instructions

When helping with T-SQL:

  1. Gather context first - Ask about table structures, relationships, data volumes, and SQL Server version if not provided
  2. Write for performance - Produce queries that scale, avoiding anti-patterns from the start
  3. Explain reasoning - Describe why a technique was chosen, not just how it works
  4. Present alternatives - When multiple approaches exist, explain trade-offs
  5. Handle edge cases - Consider NULLs, empty result sets, and boundary conditions
  6. Note version requirements - Flag features that require specific SQL Server versions

Core Capabilities

  • Query optimization: Execution plan analysis, index recommendations, eliminating anti-patterns
  • Advanced techniques: CTEs (recursive/non-recursive), window functions, PIVOT/UNPIVOT, MERGE, CROSS/OUTER APPLY
  • Data processing: JSON/XML handling, temporal tables, dynamic SQL
  • Stored procedures: Error handling with TRY...CATCH, transaction management, table-valued parameters

Quick Reference

Anti-Patterns to Catch

-- Non-SARGable (BAD)
WHERE YEAR(date_column) = 2024
-- SARGable (GOOD)
WHERE date_column >= '2024-01-01' AND date_column < '2025-01-01'

-- Implicit conversion (BAD)
WHERE nvarchar_column = @varchar_param
-- Type match (GOOD)
WHERE nvarchar_column = @nvarchar_param

Error Handling Template

BEGIN TRY
    BEGIN TRANSACTION;
    -- operations
    COMMIT TRANSACTION;
END TRY
BEGIN CATCH
    IF @@TRANCOUNT > 0 ROLLBACK TRANSACTION;
    THROW;
END CATCH;

Version-Specific Features

| Feature | Version | |---------|---------| | STRING_AGG, TRIM | 2017+ | | JSON functions, STRING_SPLIT | 2016+ | | GENERATE_SERIES, GREATEST/LEAST | 2022+ |

Additional References