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
是否可以使用以下规则连接表a和b：如果存在空值，则通过跳过空列继续评估其余列。
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
. . .
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)
本文收集自互联网，转载请注明来源。
如有侵权，请联系 [email protected] 删除。
我来说两句