MySQL 分組百分比是指在使用GROUP BY進行分組查詢的基礎上，統計每個組所占總數的百分比。

以下是一個演示MySQL分組百分比的示例，假設有如下表tb_score:

CREATE TABLE tb_score (
id INT PRIMARY KEY,
name VARCHAR(20),
subject VARCHAR(20),
score INT
);

向該表中插入數據：

INSERT INTO tb_score VALUES (1, '張三', '語文', 90);
INSERT INTO tb_score VALUES (2, '張三', '數學', 80);
INSERT INTO tb_score VALUES (3, '李四', '語文', 70);
INSERT INTO tb_score VALUES (4, '李四', '數學', 85);
INSERT INTO tb_score VALUES (5, '王五', '語文', 95);

現在要統計每個學生的語文成績和數學成績之和，以及每個科目所占成績總和的百分比。

SELECT
name,
SUM(IF(subject='語文',score,0)) AS ChineseScore,
SUM(IF(subject='數學',score,0)) AS MathScore,
ROUND(SUM(IF(subject='語文',score,0))/(SELECT SUM(score) FROM tb_score)*100,2) AS ChinesePercent,
ROUND(SUM(IF(subject='數學',score,0))/(SELECT SUM(score) FROM tb_score)*100,2) AS MathPercent
FROM
tb_score
GROUP BY
name;

輸出結果：

+------+--------------+----------+---------------+------------+
| name | ChineseScore | MathScore | ChinesePercent | MathPercent |
+------+--------------+----------+---------------+------------+
| 張三 | 90           | 80       | 40.91         | 36.36      |
| 李四 | 70           | 85       | 31.82         | 38.64      |
| 王五 | 95           | 0        | 43.18         | 0           |
+------+--------------+----------+---------------+------------+

通過以上查詢，可以看到每個學生的語文成績和數學成績之和，以及每個科目所占成績總和的百分比。