98 lines
2.5 KiB
Markdown
98 lines
2.5 KiB
Markdown
# 💎 水晶男孩推廣部：SQL 三日修煉手冊
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> **任務清單 (SOP)**
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> * style(file): 檔案命名為 .md
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> * fix(db): 確保最後不帶多餘逗號
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> * perf(save): 隨手 Ctrl + S 存檔
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---
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## 📅 DAY 1：連連看基礎 (JOIN)
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**邏輯**：用 album_id 把「歌曲」與「專輯」黏起來。
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### 1. 傳統連表 (WHERE)
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```sql
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SELECT songs.title, albums.title
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FROM songs, albums
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WHERE songs.album_id = albums.id
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ORDER BY songs.id;
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```
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### 2. 標準內連線 (INNER JOIN)
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```sql
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SELECT songs.title, albums.title
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FROM songs
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INNER JOIN albums ON songs.album_id = albums.id
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ORDER BY songs.id;
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```
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### 3. 左外連線 (LEFT JOIN)
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```sql
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SELECT songs.title, albums.title
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FROM songs
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LEFT JOIN albums ON songs.album_id = albums.id;
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```
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### 4. 右外連線 (RIGHT JOIN)
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```
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SELECT songs.title, albums.title
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FROM songs
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RIGHT JOIN albums ON songs.album_id = albums.id;
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```
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## 📅 DAY 2：資料美化與彙整
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**邏輯**：處理空值與統計數量。
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### 1. 處理空值 (IFNULL)
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```sql
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SELECT
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IFNULL(songs.title, '未命名') AS '歌名',
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IFNULL(albums.title, '未知') AS '專輯'
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FROM songs
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RIGHT JOIN albums ON songs.album_id = albums.id;
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```
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### 2. 分組統計 (COUNT)
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```sql
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SELECT
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albums.title AS '專輯名稱',
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COUNT(songs.id) AS '歌曲總數'
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FROM albums
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LEFT JOIN songs ON albums.id = songs.album_id
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GROUP BY albums.id;
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```
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## 📅 DAY 3：魔王級子查詢 (Subquery)
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### 1. 巢狀條件查詢
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```sql
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SELECT * FROM songs
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WHERE album_id = (SELECT id FROM albums WHERE title = 'Road Fighter');
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```
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-- 在每首歌後面顯示目前所有歌曲 album_id 的平均值（對比用）
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### 2.多表關聯查詢
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```sql
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-- 邏輯：同時連三張表（歌曲、專輯、成員）
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SELECT
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songs.title AS '歌名',
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albums.title AS '專輯名稱',
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albums.release_date AS '發行日期'
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FROM
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songs,
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albums
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WHERE
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songs.album_id = albums.id AND
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albums.id = 1; -- 這裡的 1 代表第一張專輯（對應老師的 dept=1）
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```
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### 3. 計算式子查詢
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```sql
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SELECT
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title,
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album_id,
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(SELECT AVG(album_id) FROM songs) AS '全庫平均編號'
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FROM
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songs;
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```
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## 🛠 努比的開發 SOP 筆記
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- **feat(db)**: 修改語法後先按 `Ctrl + S` 存檔。
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- **style(code)**: 關鍵字大寫，欄位名小寫。
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- **fix(db)**: 確保最後一個欄位沒有多餘的逗號。
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- **perf(note)**: 執行成功後，截圖貼到你的筆記網站。 |