SQL Master

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At a glance

What it is

Advanced SQL expertise including window functions, CTEs, recursive queries, query optimization with EXPLAIN plans, indexing strategies, pivot/unpivot operations, JSON operations, full-text search, stored procedures, and identification of performance anti-patterns across PostgreSQL, MySQL, and SQL Server.

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File: SKILL.md
Length: 525 lines2,148 words, about 10 min read
Category: Data engineeringpipelines and ETL
Level: Advanced
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SQL Master

Overview

This skill provides deep expertise in advanced SQL techniques that separate production-grade database work from basic querying. It covers the full spectrum from analytical window functions through query optimization, enabling you to write SQL that is both correct and performant at scale.

Window Functions

Window functions operate over a set of rows related to the current row without collapsing the result set. They are essential for ranking, running totals, moving averages, and gap-and-island analysis.

Ranking Functions

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Join Type	Best When	Cost
Nested Loop	Small outer table, indexed inner	O(n * m) worst, O(n * log m) with index
Hash Join	No useful indexes, equality joins	O(n + m) but needs memory
Merge Join	Both inputs sorted or indexable	O(n + m) but needs sorting

SQL Master

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SQL Master

Overview

Window Functions

Ranking Functions

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SQL Master

More data engineering skills.

The full skill.

SQL Master

Overview

Window Functions

Ranking Functions

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Questions.

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About this skill.

Offset Functions

Frame Specifications

Common Table Expressions (CTEs)

Standard CTEs

Recursive CTEs

Gap and Island Analysis

Query Optimization

Reading EXPLAIN Plans

Join Strategy Selection (Internal Optimizer Logic)

Statistics and Cardinality

Indexing Strategies

Index Type Decision Tree

Composite Index Design

Index Maintenance

Pivot and Unpivot Operations

JSON Operations

Full-Text Search

Stored Procedures and Functions

Performance Anti-Patterns

The Deadly Seven

Query Rewriting Patterns

Advanced Techniques

GROUPING SETS, CUBE, and ROLLUP

Materialized Views

Lateral Joins

Decision Framework

When to Use

Output Format

Example

Edge Cases