MySQL group by子句中使用with rollup作用

group by子句使用WITH ROLLUP关键字之后，在所有查询出的分组记录之后增加一条记录，该记录计算查询出的所有记录的总数，即统计记录数量。

创建测试表：

create table tb_test
(
  id   int auto_increment primary key,
  name varchar(20) null,
  age  decimal(11) null,
  year int(4)      null,
  score int(3)
);

插入数据：

insert into tb_test(name, age, year, score) values ('cj1', 3, 2016, 85), ('cj2', 4, 2015, 90), ('cj3', 5, 2014, 95);

• 执行查询：select * from tb_test;
  
• 执行查询：select name, SUM(score) FROM tb_test GROUP BY name;
  
• 执行查询：select name, SUM(score) FROM tb_test GROUP BY name WITH ROLLUP;
  
• 可使用mysql函数处理查询结果展示：

SELECT ifnull(name, 'total') AS 'total',SUM(score) FROM tb_test GROUP BY name WITH ROLLUP;
SELECT coalesce(name, 'total') AS 'total', SUM(score) FROM tb_test GROUP BY name WITH ROLLUP;

结果：