147 lines
4.1 KiB
Markdown
147 lines
4.1 KiB
Markdown
---
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name: postgres-patterns
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description: PostgreSQL 資料庫模式，涵蓋查詢優化、架構設計、索引及安全性。基於 Supabase 最佳實踐。
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---
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# PostgreSQL 模式 (PostgreSQL Patterns)
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PostgreSQL 最佳實踐快速參考指南。如需更深入的建議，請使用 `database-reviewer` Agent。
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## 何時啟用
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- 編寫 SQL 查詢或進行資料遷移 (Migrations)。
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- 設計資料庫架構 (Schemas)。
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- 排除查詢緩慢的故障。
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- 實作資料列層級安全性 (Row Level Security, RLS)。
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- 設置連接池。
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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` | 複合索引 (Composite) | `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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| 時間序列區間 (Ranges) | BRIN | `CREATE INDEX idx ON t USING brin (col)` |
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### 資料型別快速對比
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| 使用場景 | 正確型別 | 應避免使用 |
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|----------|-------------|-------|
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| ID 欄位 | `bigint` | `int`, 隨機 UUID |
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| 字串 | `text` | `varchar(255)` |
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| 時間戳記 | `timestamptz` | `timestamp` |
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| 金額 | `numeric(10,2)` | `float` |
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| 旗標 (Flags) | `boolean` | `varchar`, `int` |
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### 常見模式
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**複合索引排序規則：**
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```sql
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-- 先放等值 (Equality) 欄位，再放範圍 (Range) 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 (Covering Index)：**
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```sql
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CREATE INDEX idx ON users (email) INCLUDE (name, created_at);
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-- 針對 SELECT email, name, created_at，可避免回表查詢 (Table lookup)
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```
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**部分索引 (Partial Index)：**
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```sql
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CREATE INDEX idx ON users (email) WHERE deleted_at IS NULL;
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-- 體積較小，僅包含活躍中的使用者
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```
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**RLS 策略（優化版）：**
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```sql
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CREATE POLICY policy ON orders
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USING ((SELECT auth.uid()) = user_id); -- 務必包裹在 SELECT 中！
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```
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**更新或插入 (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 (Cursor Pagination)：**
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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) 複雜度；相比之下 OFFSET 為 O(n)
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```
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**隊列處理 (Queue Processing)：**
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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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-- 找出未建立索引的外鍵 (Unindexed Foreign Keys)
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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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-- 找出查詢緩慢的 SQL
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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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-- 檢查資料表膨脹 (Bloat) 情況
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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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### 配置範本
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```sql
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-- 連線限制（視記憶體大小調整）
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ALTER SYSTEM SET max_connections = 100;
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ALTER SYSTEM SET work_mem = '8MB';
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-- 超時設定
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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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-- 安全性預設值
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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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## 相關連結
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- Agent: `database-reviewer` - 完整的資料庫審查工作流。
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- 技能: `clickhouse-io` - ClickHouse 分析模式。
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- 技能: `backend-patterns` - API 與後端模式。
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---
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*源自 [Supabase Agent Skills](https://github.com/supabase/agent-skills) (MIT License)*
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