选择总值及其子集

Question

我有一张表，不同国家的值不同，例如：

编号|国家 |价值 ==================== 1 |阿格利亚 | 8 2 |美国 | 10 1 |中国 | 12 1 |意大利 | 13

我只对一个国家/地区和总数感兴趣，但我无法提出一个查询来完成它。 id 1 的查询结果为：

编号| value_in_意大利 |全部的 =========================== 1 | 13 | 33

如您所见，我获得了意大利的价值和总价值。对于类似的表，什么样的查询会产生像上面这样的行？

Answer 1

这是您需要的查询：

select id,SUM(IF(country='Italy',value,0)) italy_value,SUM(value) id_values
from countrydata where id = 1;

这是您的示例数据：

drop database if exists luqita;
create database luqita;
use luqita
create table countrydata
(
    id int not null,
    country varchar(32),
    value int not null
);
insert into countrydata values
(1,'Argelia',  8 ),(2,'USA'    , 10 ),
(1,'China'  , 12 ),(1,'Italy'  , 13 );
select * from countrydata;

这是您加载的示例数据：

mysql> drop database if exists luqita;
Query OK, 1 row affected (0.03 sec)

mysql> create database luqita;
Query OK, 1 row affected (0.02 sec)

mysql> use luqita
Database changed
mysql> create table countrydata
    -> (
    ->     id int not null,
    ->     country varchar(32),
    ->     value int not null
    -> );
Query OK, 0 rows affected (0.12 sec)

mysql> insert into countrydata values
    -> (1,'Argelia',  8 ),(2,'USA'    , 10 ),
    -> (1,'China'  , 12 ),(1,'Italy'  , 13 );
Query OK, 4 rows affected (0.05 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> select * from countrydata;
+----+---------+-------+
| id | country | value |
+----+---------+-------+
|  1 | Argelia |     8 |
|  2 | USA     |    10 |
|  1 | China   |    12 |
|  1 | Italy   |    13 |
+----+---------+-------+
4 rows in set (0.00 sec)   

mysql>

这是执行的建议查询：

mysql> select id,SUM(IF(country='Italy',value,0)) italy_value,SUM(value) id_values
    -> from countrydata where id = 1;
+----+-------------+-----------+
| id | italy_value | id_values |
+----+-------------+-----------+
|  1 |          13 |        33 |
+----+-------------+-----------+
1 row in set (0.00 sec)

mysql>

现在，如果您想同时针对所有行运行此查询，请尝试以下全包式查询：

select
    B.id,
    SUM(IF(A.country=B.country,B.value,0)) country_value,
    SUM(IF(A.id=B.id,A.value,0)) id_values
from
    countrydata A,
    countrydata B
group by B.country;

这里是执行包罗万象的查询

mysql> select
    ->     B.id,
    ->     SUM(IF(A.country=B.country,B.value,0)) country_value,
    ->     SUM(IF(A.id=B.id,A.value,0)) id_values
    -> from
    ->     countrydata A,
    ->     countrydata B
    -> group by B.country;
+----+---------------+-----------+
| id | country_value | id_values |
+----+---------------+-----------+
|  1 |             8 |        33 |
|  1 |            12 |        33 |
|  1 |            13 |        33 |
|  2 |            10 |        10 |
+----+---------------+-----------+
4 rows in set (0.00 sec)

mysql>

试试看！！！