query-missing-indexes

Queries filtering or joining on unindexed columns cause full table scans, which become exponentially slower as tables grow.

Skills
Databases
0

What it does and how to use it

A skill that teaches Claude Code to do databases tasks well. It is packaged knowledge the model uses whenever it is relevant.

Install the skill (command above).
In Claude Code, describe what you need - the skill turns on by itself when the context fits.
No commands to memorize: you talk in plain language and the skill does the rest.

Install (Claude Code)

mkdir -p .claude/skills/query-missing-indexes && curl -fsSL https://doutorai.pt/data/lib/skills__query-missing-indexes.md -o .claude/skills/query-missing-indexes/SKILL.md

Paste this command into the terminal, in your project folder, and the component installs automatically.

Content

---
title: Add Indexes on WHERE and JOIN Columns
impact: CRITICAL
impactDescription: 100-1000x faster queries on large tables
tags: indexes, performance, sequential-scan, query-optimization
---

## Add Indexes on WHERE and JOIN Columns

Queries filtering or joining on unindexed columns cause full table scans, which become exponentially slower as tables grow.

**Incorrect (sequential scan on large table):**

```sql
-- No index on customer_id causes full table scan
select * from orders where customer_id = 123;

-- EXPLAIN shows: Seq Scan on orders (cost=0.00..25000.00 rows=100 width=85)
```

**C

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