sql-optimizer

A skill for analyzing and improving slow SQL queries. SQL is the language used to read and change data in relational databases.

In plain words
What is it for?
Understanding a query, detecting performance problems, recommending indexes, and producing a rewritten query for the relevant database system.
Why use it?
It helps identify inefficient query patterns, poor joins, missing indexes, and other causes of slow database work.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/adityawrk/analytics-with-claude-code/sql-optimizer
Any agent
npx skills add adityawrk/analytics-with-claude-code --skill sql-optimizer
Clone the repo
git clone --depth 1 https://github.com/adityawrk/analytics-with-claude-code

Made for: Claude Code, Codex.

Per session 63 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,218 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00063 $0.02218
Opus 5 $0.00032 $0.01109
Sonnet 5 $0.00013 $0.00444
Haiku 4.5 $0.00006 $0.00222

Measured 2d ago against content hash b9453a5bd4ca, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

sql-optimizer scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/skills/sql-optimizer/SKILL.md · 210 lines

How it starts

The opening of the file, as written. The whole thing — 210 lines — stays where its author put it; the contents beside it link to each section on GitHub.

SQL Query Optimizer

You are a senior database performance engineer. When given a SQL query, you will perform a comprehensive optimization analysis and produce a rewritten, optimized version. Follow every step below.

Step 1: Parse and Understand the Query

Before optimizing, fully understand the query:

  1. Identify the query type: SELECT, INSERT...SELECT, UPDATE, DELETE, MERGE, or CTE chain.
  2. Map the table graph: list every table and alias, how they are joined (INNER, LEFT, RIGHT, FULL, CROSS), and the join predicates.
  3. Identify the intent: write a one-sentence plain-English description of what the query is trying to accomplish.
  4. Note the database dialect: determine from syntax whether this is PostgreSQL, MySQL, BigQuery, Snowflake, Redshift, SQL Server, SQLite, or standard SQL. Ask the user if ambiguous. This affects optimization recommendations.

Step 2: Anti-Pattern Detection

Check for each of the following anti-patterns. For each one found, explain WHY it is a problem and provide the fix.

2.1 SELECT * Usage

  • Problem: fetches unnecessary columns, increases I/O, prevents covering index usage.
  • Fix: replace with explicit column list. If the user does not know which columns are needed, ask.

2.2 Missing or Weak WHERE Clauses

  • Problem: full table scans on large tables.
  • Fix: add appropriate filters. Flag queries on tables likely to be large (fact tables, event logs, transactions) that have no WHERE or LIMIT.

2.3 Implicit Type Conversions

  • Problem: WHERE varchar_col = 123 forces a cast on every row, preventing index usage.
  • Fix: match the literal type to the column type.

2.4 Functions on Indexed Columns

  • Problem: WHERE DATE(created_at) = '2024-01-01' cannot use an index on created_at.
  • Fix: rewrite as range: WHERE created_at >= '2024-01-01' AND created_at < '2024-01-02'.

2.5 Correlated Subqueries

  • Problem: execute once per row in the outer query.
  • Fix: rewrite as JOIN or use a CTE. Show the rewrite.

Read the full file on GitHub · 210 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 210 lines · 63 tokens per session scan A b9453a5bd4ca

Subscribe to this mod's changes

sql-optimizer is a skill published in the GitHub repository adityawrk/analytics-with-claude-code (5 stars, last pushed 6mo ago), licensed MIT. It adds 63 tokens to every session and 2,218 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

Related

Other skills, from other repositories

pr-verify

Verify a Docglow change actually works before submitting or merging a PR. Runs the conformance suite, then a behavioral verification pass (flag matrix, artifact-join spot checks, pipeline contract sweep, payload budget). Use when reviewing a PR, self-reviewing a branch before opening a PR, or when asked to "verify…

docglow/docglow · 79 tokens

developing-incremental-models

Develops and troubleshoots dbt incremental models. Use when working with incremental materialization for: (1) Creating new incremental models (choosing strategy, uniquekey, partition) (2) Task mentions "incremental", "append", "merge", "upsert", or "late arriving data" (3) Troubleshooting incremental failures (merge…

AltimateAI/data-engineering-skills · 112 tokens

altimate-code

Delegates dbt and warehouse work to altimate-code, a specialized CLI agent with 100+ purpose-built data tools. USE THIS SKILL FIRST whenever the task mentions or implies: warehouse access (Snowflake, BigQuery, Redshift, Databricks, Postgres, MySQL, DuckDB), column-level lineage, downstream-impact analysis, dbt builds…

AltimateAI/data-engineering-skills · 184 tokens

debugging-dbt-errors

Debugs and fixes dbt errors systematically. Use when working with dbt errors for: (1) Task mentions "fix", "error", "broken", "failing", "debug", "wrong", or "not working" (2) Compilation Error, Database Error, or test failures occur (3) Model produces incorrect output or unexpected results (4) Need to troubleshoot…

AltimateAI/data-engineering-skills · 112 tokens

documenting-dbt-models

Documents dbt models and columns in schema.yml. Use when working with dbt documentation for: (1) Adding model descriptions or column definitions to schema.yml (2) Task mentions "document", "describe", "description", "dbt docs", or "schema.yml" (3) Explaining business context, grain, meaning of data, or business rules…

AltimateAI/data-engineering-skills · 105 tokens

refactoring-dbt-models

Safely refactors dbt models with downstream impact analysis. Use when restructuring dbt models for: (1) Task mentions "refactor", "restructure", "extract", "split", "break into", or "reorganize" (2) Extracting CTEs to intermediate models or creating macros (3) Modifying model logic that has downstream consumers (4)…

AltimateAI/data-engineering-skills · 108 tokens