我希望左外连接在。:/ / p>之间有一个n:m连接表
Table A
column: id_a
Table A:B
column: id_a
column: id_b
Table B
column: id_b
表b包含所有可能的行。因此,列B必须在左侧。
我无法弄清楚如何呈现以显示1表A的所有可能值。我想显示所有的entires和误导的(为什么离开外部)
使用MySql
示例数据。
篮子(表A)
1 | basket x
2 | basket y
水果(表B)
1 | apple
2 | strawberries
3 | grapes
4 | lemon
连接表
1 | 1
1 | 2
2 | 1
2 | 2
2 | 3
结果 篮子X查询的结果
1 | 1
1 | 2
1 | 3 (something which indicates it is not assigned . since there is no connection )
1 | 4 (something which indicates it is not assigned . since there is no connection )
答案 0 :(得分:0)
我认为您需要cartesian
结果。请考虑以下示例
declare @baskets table(basket_id int not null primary key identity, basketName varchar(255));
declare @fruits table(fruit_id int not null primary key identity, fruitName varchar(255));
declare @basketsFruits table(basket_id int not null, fruit_id int not null);
insert into @baskets(basketName)
values('basket x'), ('basket y');
insert into @fruits(fruitName)
values('apple'), ('strawberries'), ('grapes'), ('lemon');
insert into @basketsFruits(basket_id, fruit_id)
values(1, 1), (1, 2), (2, 1), (2, 2), (2, 3);
select b.*, f.fruitName
, case when exists(select 1 from @basketsFruits as bf where bf.basket_id = b.basket_id and bf.fruit_id = f.fruit_id) then
'Fruit Present'
else
'Fruit not Present'
end as fruitStatus
from @baskets as b, @fruits as f -- cartesian all the fruits and all the baskets
where b.basket_id = 1
<强>结果:强>