SQL Skills

Comprehensive SQL skill suite covering query writing, optimization, debugging, analytics, and cross-dialect translation.

Overview

This skill provides guidance for all SQL-related tasks across major database systems (PostgreSQL, MySQL, SQL Server, Oracle, SQLite). Use when writing queries, optimizing performance, debugging issues, or translating between dialects.

Trigger Conditions

Activate this skill when the user:

• •Asks to write, create, or generate SQL queries
• •Needs help with SELECT, INSERT, UPDATE, DELETE, or DDL statements
• •Wants to optimize slow queries or improve database performance
• •Has SQL errors or unexpected query results
• •Needs to understand or explain complex queries
• •Wants to translate SQL between database dialects
• •Requires window functions, CTEs, or advanced SQL features
• •Needs analytics, reporting, or data quality queries

Sub-Skills Directory

Skill Selection Logic

User Request -> Analyze Intent -> Select Appropriate Sub-Skill

"Write a query to..." -> query-writer
"Check this SQL..." -> syntax-checker
"Explain this query..." -> query-explainer
"This query is slow..." -> optimizer or performance-tuning
"Why is this failing..." -> debugger
"I need a ranking..." -> window-functions
"Convert this to PostgreSQL..." -> dialect-translator
"Check for duplicate data..." -> data-quality
"Create a monthly report..." -> reporting
"Calculate running total..." -> window-functions or analytics-sql

Supported Database Dialects

Query Structure Reference

SELECT Statement Components

SELECT [DISTINCT] columns
FROM table
[JOIN other_table ON condition]
[WHERE filter_condition]
[GROUP BY grouping_columns]
[HAVING aggregate_condition]
[ORDER BY sort_columns]
[LIMIT n OFFSET m]

Common Clause Order

1. •SELECT - What columns to return
2. •FROM - Source table(s)
3. •JOIN - Additional tables with relationships
4. •WHERE - Row-level filtering (before grouping)
5. •GROUP BY - Aggregate grouping
6. •HAVING - Aggregate filtering (after grouping)
7. •ORDER BY - Result sorting
8. •LIMIT/OFFSET - Pagination

Best Practices Summary

Query Writing

• •Use explicit column names, avoid SELECT *
• •Alias tables and complex expressions
• •Use parameterized queries to prevent SQL injection
• •Format queries for readability

Performance

• •Index columns used in WHERE, JOIN, ORDER BY
• •Avoid functions on indexed columns in WHERE
• •Use EXISTS instead of IN for subqueries
• •Limit result sets with appropriate filtering

Maintainability

• •Use CTEs for complex multi-step queries
• •Add meaningful aliases
• •Break complex logic into views or functions
• •Document business logic in comments

Error Handling Pattern

-- PostgreSQL
BEGIN;
    -- your queries here
    IF condition THEN
        RAISE EXCEPTION 'Error message';
    END IF;
COMMIT;

-- SQL Server
BEGIN TRY
    BEGIN TRANSACTION;
    -- your queries here
    COMMIT TRANSACTION;
END TRY
BEGIN CATCH
    ROLLBACK TRANSACTION;
    THROW;
END CATCH;

Quick Reference Cards

Aggregation Functions

JOIN Types

Common Operators

Validation Checklist

Before outputting any SQL:

• • Syntax is valid for target dialect
• • Table and column names exist
• • JOIN conditions are complete (no cartesian products)
• • WHERE clause has appropriate filters
• • GROUP BY includes all non-aggregated columns
• • ORDER BY columns are in SELECT or valid
• • Parameters are properly escaped/parameterized
• • Query handles NULL values appropriately