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.
npx skills add jiushiwon/wg-skills --skill database-learning-skillgit clone --depth 1 https://github.com/jiushiwon/wg-skillsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/jiushiwon/wg-skills/database-learning-skill)<a href="https://agentmods.dev/skills/jiushiwon/wg-skills/database-learning-skill"><img src="https://agentmods.dev/badge/skills/jiushiwon/wg-skills/database-learning-skill/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/jiushiwon/wg-skills/database-learning-skill"><img src="https://agentmods.dev/badge/skills/jiushiwon/wg-skills/database-learning-skill.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00101 | $0.01965 |
| Opus 5 | $0.00051 | $0.00983 |
| Sonnet 5 | $0.00020 | $0.00393 |
| Haiku 4.5 | $0.00010 | $0.00197 |
Grade A, and why
database-learning-skill 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 5d 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.
How it starts
The opening of the file, as written. The whole thing — 232 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Database Learning Skill
面向零基础学习者，系统学习数据库核心概念，掌握数据库选型与优化能力。
核心理念
数据库 = 数据的仓库 + 管理的艺术
学数据库不是背命令，而是理解：
- 数据如何组织（表结构）
- 数据如何关联（关系）
- 数据如何高效查找（索引）
- 数据如何安全（事务）
- 什么场景选什么数据库（选型）
学习路径
数据库入门
↓
表结构设计（数据结构）
↓
数据查询（SQL 基础）
↓
索引与查询优化
↓
事务与并发控制
↓
MySQL vs PostgreSQL 选型
学习模块
1. 数据结构（表设计）
| 概念 | 说明 |
|---|---|
| 表（Table） | 数据的二维表格，像 Excel |
| 字段（Column） | 表的列，如 id、name、age |
| 记录（Row） | 表的行，一条数据 |
| 主键（Primary Key） | 唯一标识一条记录 |
| 外键（Foreign Key） | 表与表的关联 |
| 约束 | 数据的规则（唯一、非空、默认值） |
实战：设计一个用户表、一个订单表
2. SQL 查询
| 操作 | SQL 关键字 |
|---|---|
| 查询 | SELECT |
| 插入 | INSERT |
| 更新 | UPDATE |
| 删除 | DELETE |
| 条件 | WHERE |
| 排序 | ORDER BY |
| 分组 | GROUP BY |
| 聚合 | COUNT/SUM/AVG/MAX/MIN |
3. 索引（核心）
为什么需要索引？
无索引：逐行扫描 → 10万行 = 10万次 IO
有索引：B+Tree 定位 → 10万行 ≈ 3次 IO
| 索引类型 | 说明 | 适用场景 |
|---|---|---|
| 主键索引 | 自动唯一，非空 | 主键字段 |
| 唯一索引 | 字段值唯一 | username、email |
| 普通索引 | 加速查找 | 常用查询字段 |
| 复合索引 | 多字段组合 | 多条件查询 |
| 全文索引 | 文本搜索 | 文章内容搜索 |
最左前缀原则：复合索引 (a, b, c) 能命中 a、a+b、a+b+c，不能命中 b、c
4. 事务（核心）
什么是事务？
事务 = 一组 SQL 操作，要么全部成功，要么全部失败
转账场景：
1. A 账户 -1000
2. B 账户 +1000
必须一起成功或一起失败
ACID 特性
| 特性 | 说明 |
|---|---|
| Atomic（原子性） | 不可分割，要么全成功要么全失败 |
| Consistency（一致性） | 事务前后数据状态一致 |
| Isolation（隔离性） | 并发事务互不干扰 |
| Durability（持久性） | 提交后数据永久保存 |
隔离级别
| 级别 | 脏读 | 不可重复读 | 幻读 |
|---|---|---|---|
| 读未提交 | 有 | 有 | 有 |
| 读已提交 | 无 | 有 | 有 |
| 可重复读 | 无 | 无 | 有 |
| 串行化 | 无 | 无 | 无 |
MySQL 默认：可重复读（RR） PostgreSQL 默认：读已提交（RC）
5. 查询优化
慢查询分析
-- 开启慢查询日志
SHOW VARIABLES LIKE 'slow_query_log';
-- 查看慢查询
SELECT * FROM slow_log ORDER BY start_time DESC LIMIT 10;
-- 使用 EXPLAIN 分析查询
EXPLAIN SELECT * FROM users WHERE username = 'test';
优化技巧
- **避免 SELECT *** → 只查询需要的字段
- 避免函数运算 → WHERE age * 2 > 30 改为 WHERE age > 15
- 避免隐式转换 → '123' vs 123
- 使用索引 → 确保 WHERE 条件有索引
- 分页优化 → SELECT * FROM users LIMIT 100000, 10 改为 WHERE id > last_id
What ships with it
6 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 5d ago First seen · 232 lines · 101 tokens per session scan A 2f764dc945c0
database-learning-skill is a skill published in the GitHub repository jiushiwon/wg-skills (102 stars, last pushed 2d ago), licensed Apache-2.0. It adds 101 tokens to every session and 1,965 once invoked, about $0.0005 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 2026-09-07.
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