MySQL左连接的总和与关系1：X

Question

好的，首先，我要更改表、字段和值的名称，我只是保留我的数据库的结构以供您理解。

现在，假设我有一个表people，其中包含id、age、country 和language 字段。还有另一张桌子foods，桌子上的每个人都吃过食物people，字段：person_id，food，units。 注意：food 是char，不是另一个表的 ID，我无法更改此结构。

现在，让我们放一些数据：

.

人

ID | AGE | COUNTRY | LANGAGE
1  |  25 |   usa   |  en
2  |  46 |   mex   |  es

.

食物

ID | PERSON_ID | FOOD  | UNITS
1  |     1     | apple |   2
2  |     1     | grape |  24
3  |     1     | pizza |   1
4  |     2     | apple |   3
5  |     2     | pizza |   2

.

好的，我需要得到id、age、country 以及apple 和grape 的总和被一个人吃掉（忽略pizza）。在这个例子中，如果我查找 ID 1，我应该得到：

ID | AGE | COUNTRY | UNITS 
1  |  25 |   usa   | 26

对于 ID 2：

ID | AGE | COUNTRY | UNITS 
2  |  46 |   mex   | 3

Answer 1

http://sqlfiddle.com/#!9/38304/2

SELECT p.*, SUM(f.units)
FROM people p
LEFT JOIN foods f
ON f.person_id = p.id
  AND f.food in('apple','grape')
GROUP BY p.id

Answer 2

select p.id, p.age, p.country, sum(f.units) as units
from people p join foods f
on (p.id = foods.person_id and f.food in ('apple', 'grape'))
group by p.id, p.age, p.country

如果您需要其他食物组合，只需编辑in 子句的内容即可。

Answer 3

SELECT p.Id, p.Age,p.country, sum(f.units)
FROM people AS p
INNER JOIN foods AS f ON f.person_id = p.id
WHERE f.food <> 'Pizza'
GROUP BY p.id,p.age,p.country

Answer 4

select 
t1.id, t1.age, t1.country, sum(t2.units)
from people as t1, foods as t2
where 
t1.id = t2.person_id and t2.food != 'pizza'
group by t1.id 
order by t1.id

Answer 5

select p.id, p.age, p.country, sum(f.units) as units 
from people p 
join foods f on f.person_id = p.id 
where f.food <> 'Pizza' 
group by p.id, f.food