Sql 从左jon中排除Null

我已经加入了2个表左连接

Select a.Invoice,
       b.Prodict
From table1 a
left join table2 b
on a.Id = b.Id

我想说的是，如果一张发票有两个或更多的产品，那么排除空值，如果只有空值，那么保持空值。 多谢各位

---

有福了。

我认为您需要过滤第二个表，使其不包含空值

Select a.Invoice,
       b.Prodict
From table1 a
left join table2 b
on a.Id = b.Id and b.Prodict is not null

---

嗯。数据中似乎有

NULL

值。我建议在

左连接中过滤掉它们

本身：

Select a.Invoice,
       b.Product
From table1 a left join
     table2 b
     on a.Id = b.Id and b.Product is not null;

唯一的

NULL

s将是由

左连接生成的：

此解决方案的唯一问题是，如果希望从
b
中选择其他列，并且有一个匹配行
NULL
。使用此解决方案，其他列将为
NULL

如果这是您的实际问题，请使用示例数据和所需结果提出一个新问题。
您需要确定
表2中
产品
列中的
空
发票是否有任何非空
行

如果您的DBMS具有分析功能，则可以使用它：

发票|产品
:------ | :------
A | AA
A | AB
B|BA
B | BB
C |空
dbfiddle
使用您正在使用的数据库标记您的问题。请提供一些。如果我将产品设置为非空，则会排除一些只有空值的发票。例如，如发票号码4@Hanry_Lou不，不会的：）你们自己试试吧。请注意，筛选器处于联接条件，而不是where条件。我的表1有450M条记录，联接后返回15M条记录。很难跟踪每一行。
LEFT JOIN
不会从左侧的源代码中删除任何内容，因此我无法想象它可以减少生成的行数。只要不清楚
发票
、
Id
和
产品
之间的关系，并且没有任何DBMS标记，我就添加了这个通用答案。否则，上面有好的和简短的答案
with table1 as (
  select 1 as id, 'A' as Invoice union all
  select 2 as id, 'B' as Invoice union all
  select 3 as id, 'B' as Invoice union all
  select 4 as id, 'C' as Invoice
)
, table2 as (
  select 1 as id, 'AA' as Product union all
  select 1 as id, 'AB' as Product union all
  select 2 as id, 'BA' as Product union all
  select 2 as id, NULL as Product union all
  select 2 as id, 'BB' as Product
)
, find_null as (
Select
  a.Invoice,
  b.Product,
  /*Check if NULL is here*/
  max(case when b.Product is null then 1 end) over(partition by a.Invoice) as has_null,
  /*Count not null values*/
  count(b.Product) over(partition by a.Invoice) as item_cnt
From table1 a
  left join table2 b
    on a.Id = b.Id
)
select invoice, product
from find_null
where not (
  has_null = 1
  and item_cnt > 0
  /*Exclude null where there's a row without null*/
  and product is null
)
GO

invoice | product
:------ | :------
A       | AA     
A       | AB     
B       | BA     
B       | BB     
C       | null
with table1 as (
  select 1 as id, 'A' as Invoice union all
  select 2 as id, 'B' as Invoice union all
  select 3 as id, 'B' as Invoice union all
  select 4 as id, 'C' as Invoice
)
, table2 as (
  select 1 as id, 'AA' as Product union all
  select 1 as id, 'AB' as Product union all
  select 2 as id, 'BA' as Product union all
  select 2 as id, NULL as Product union all
  select 2 as id, 'BB' as Product
)
Select
  a.Invoice,
  b.Product
From table1 a
  left join table2 b
    on a.Id = b.Id
where not exists (
  select 1
  from table1 f1
    join table2 f2
      on f1.id = f2.id
  where f1.invoice = a.invoice
    and f2.product is not null
    and b.Product is null
  
)
GO

Invoice | Product
:------ | :------
A       | AA     
A       | AB     
B       | BA     
B       | BB     
C       | null