Question

假设我有2张桌子

Table a
brand    Fruit         edible   color   size
farmers  banana        yes      yellow  null
fresh    banana        yes      red     10
bounty   banana        null     green   2
farmers  apple         yes      red     5
organic  grapes        null     violet  5
love     strawberry    yes      null    5
flow     lavander      no       null    null

Table b
boxId   fruit     edible    color   size
10100   banana     yes       yellow  9
19299   banana     yes       red     10
10992   apple      yes       red     5
10299   grapes     yes       red     5 
01929   lavander   no        violet  3

是否可以连接表a和b，即使规则如下：如果有空值，则通过跳过空列继续评估剩余的列。

select a.brand, b.boxId from a prod
inner join b box on a.fruit = b.fruit
where a.edible = b.edible and 
a.color = b.color and 
a.size = b.size

brand       boxID
farmers      10100
fresh        19299
. . .

Answer 1

是这样的

select a.brand, b.boxId 
from a prod
inner join b box on a.fruit = b.fruit
where ( a.edible = b.edible OR a.edible IS NULL OR b.edible IS NULL ) and 
      ( a.color = b.color OR a.color IS NULL OR b.color IS NULL ) and 
      ( a.size = b.size OR a.size IS NULL OR b.size IS NULL)

Answer 2

试试这个：

select a.brand,b.boxId from
(select a.brand,a.Fruit,a.edible,a.color,a.size from prod) as a
inner join
(select * from box) as b
 on a.fruit = b.fruit 
where a.color is not null and a.edible is not null and a.size is not null
and b.color is not null and b.edible is not null and b.size is not null

MySQL内部连接与空列

2 个答案: