求一个简单的分类汇总查询的问题

[若鱼1919]

表结构：
mysql> select * from person;
+----+------+------+
| id | name | age |
+----+------+------+
| 1 | aa | 20 |
| 2 | aa | 21 |
| 3 | aa | 18 |
| 4 | aa | 31 |
+----+------+------+

CREATE TABLE `person` (
  `id` int(11) NOT NULL,
  `name` varchar(32) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
INSERT INTO `person` VALUES (1,'aa',20),(2,'aa',21),(3,'aa',18),(4,'aa',31);

我想得到两个分组：一个是大于20的人数，一个是小于等于20的人数。
请问该怎么写？

[二月十六]

最后的结果是想2 2这样还是id name age 这样的数据?

[若鱼1919]

引用 1 楼 sinat_28984567 的回复:

最后的结果是想2 2这样还是id name age 这样的数据?

2， 2 这样的 不需要id name age 这些东西

[二月十六]

额，这样行吗？

select (select COUNT(1) from person where age>20) as 大于20人数,
(select COUNT(1)  from person where age<=20) as 小于20人数

[若鱼1919]

引用 3 楼 sinat_28984567 的回复:

额，这样行吗？

select (select COUNT(1) from person where age>20) as 大于20人数,
(select COUNT(1)  from person where age<=20) as 小于20人数

感谢！

[ACMAIN_CHM]

mysql> select * from person;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | aa   |   20 |
|  2 | aa   |   21 |
|  3 | aa   |   18 |
|  4 | aa   |   31 |
+----+------+------+
4 rows in set (0.00 sec)

mysql> select sum(age>20),sum(age<=20) from person;
+-------------+--------------+
| sum(age>20) | sum(age<=20) |
+-------------+--------------+
|           2 |            2 |
+-------------+--------------+
1 row in set (0.00 sec)

mysql>

[若鱼1919]

引用 5 楼 ACMAIN_CHM 的回复:

mysql> select * from person;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | aa   |   20 |
|  2 | aa   |   21 |
|  3 | aa   |   18 |
|  4 | aa   |   31 |
+----+------+------+
4 rows in set (0.00 sec)

mysql> select sum(age>20),sum(age<=20) from person;
+-------------+--------------+
| sum(age>20) | sum(age<=20) |
+-------------+--------------+
|           2 |            2 |
+-------------+--------------+
1 row in set (0.00 sec)

mysql>

感谢！