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147 lines
3.6 KiB
Markdown
147 lines
3.6 KiB
Markdown
---
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name: postgres-patterns
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description: PostgreSQL database patterns for query optimization, schema design, indexing, and security. Based on Supabase best practices.
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---
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# PostgreSQL 模式
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PostgreSQL 最佳實務快速參考。詳細指南請使用 `database-reviewer` agent。
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## 何時啟用
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- 撰寫 SQL 查詢或 migrations
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- 設計資料庫 schema
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- 疑難排解慢查詢
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- 實作 Row Level Security
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- 設定連線池
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## 快速參考
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### 索引速查表
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| 查詢模式 | 索引類型 | 範例 |
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|---------|---------|------|
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| `WHERE col = value` | B-tree（預設） | `CREATE INDEX idx ON t (col)` |
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| `WHERE col > value` | B-tree | `CREATE INDEX idx ON t (col)` |
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| `WHERE a = x AND b > y` | 複合 | `CREATE INDEX idx ON t (a, b)` |
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| `WHERE jsonb @> '{}'` | GIN | `CREATE INDEX idx ON t USING gin (col)` |
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| `WHERE tsv @@ query` | GIN | `CREATE INDEX idx ON t USING gin (col)` |
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| 時間序列範圍 | BRIN | `CREATE INDEX idx ON t USING brin (col)` |
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### 資料類型快速參考
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| 使用情況 | 正確類型 | 避免 |
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|---------|---------|------|
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| IDs | `bigint` | `int`、隨機 UUID |
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| 字串 | `text` | `varchar(255)` |
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| 時間戳 | `timestamptz` | `timestamp` |
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| 金額 | `numeric(10,2)` | `float` |
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| 旗標 | `boolean` | `varchar`、`int` |
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### 常見模式
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**複合索引順序：**
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```sql
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-- 等值欄位優先，然後是範圍欄位
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CREATE INDEX idx ON orders (status, created_at);
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-- 適用於：WHERE status = 'pending' AND created_at > '2024-01-01'
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```
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**覆蓋索引：**
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```sql
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CREATE INDEX idx ON users (email) INCLUDE (name, created_at);
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-- 避免 SELECT email, name, created_at 時的表格查詢
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```
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**部分索引：**
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```sql
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CREATE INDEX idx ON users (email) WHERE deleted_at IS NULL;
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-- 更小的索引，只包含活躍使用者
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```
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**RLS 政策（優化）：**
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```sql
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CREATE POLICY policy ON orders
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USING ((SELECT auth.uid()) = user_id); -- 用 SELECT 包裝！
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```
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**UPSERT：**
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```sql
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INSERT INTO settings (user_id, key, value)
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VALUES (123, 'theme', 'dark')
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ON CONFLICT (user_id, key)
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DO UPDATE SET value = EXCLUDED.value;
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```
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**游標分頁：**
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```sql
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SELECT * FROM products WHERE id > $last_id ORDER BY id LIMIT 20;
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-- O(1) vs OFFSET 是 O(n)
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```
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**佇列處理：**
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```sql
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UPDATE jobs SET status = 'processing'
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WHERE id = (
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SELECT id FROM jobs WHERE status = 'pending'
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ORDER BY created_at LIMIT 1
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FOR UPDATE SKIP LOCKED
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) RETURNING *;
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```
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### 反模式偵測
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```sql
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-- 找出未建索引的外鍵
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SELECT conrelid::regclass, a.attname
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FROM pg_constraint c
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JOIN pg_attribute a ON a.attrelid = c.conrelid AND a.attnum = ANY(c.conkey)
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WHERE c.contype = 'f'
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AND NOT EXISTS (
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SELECT 1 FROM pg_index i
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WHERE i.indrelid = c.conrelid AND a.attnum = ANY(i.indkey)
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);
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-- 找出慢查詢
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SELECT query, mean_exec_time, calls
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FROM pg_stat_statements
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WHERE mean_exec_time > 100
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ORDER BY mean_exec_time DESC;
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-- 檢查表格膨脹
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SELECT relname, n_dead_tup, last_vacuum
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FROM pg_stat_user_tables
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WHERE n_dead_tup > 1000
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ORDER BY n_dead_tup DESC;
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```
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### 設定範本
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```sql
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-- 連線限制（依 RAM 調整）
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ALTER SYSTEM SET max_connections = 100;
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ALTER SYSTEM SET work_mem = '8MB';
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-- 逾時
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ALTER SYSTEM SET idle_in_transaction_session_timeout = '30s';
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ALTER SYSTEM SET statement_timeout = '30s';
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-- 監控
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CREATE EXTENSION IF NOT EXISTS pg_stat_statements;
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-- 安全預設值
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REVOKE ALL ON SCHEMA public FROM public;
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SELECT pg_reload_conf();
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```
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## 相關
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- Agent：`database-reviewer` - 完整資料庫審查工作流程
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- Skill：`clickhouse-io` - ClickHouse 分析模式
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- Skill：`backend-patterns` - API 和後端模式
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---
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*基於 [Supabase Agent Skills](https://github.com/supabase/agent-skills)（MIT 授權）*
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