连接不同表结构的SQL（MSSQL）

我有不同的表，我想加入所有的信息。在我的例子中，我有一个产品、销售和产品定义表

产品表：

ProductID | Name
     1    | Product 1
     2    | Product 2
     3    | Product 3

产品定义表：

DefID    | ProductID |  Column 1 | Column 2 | ....
001      |   1       |    text   |   text
002      |   1       |    text   |   text       
003      |   3       |    text   |   text
004      |   2       |    text   |   text
005      |   3       |    text   |   text

销售表：

SalesID | ProductID |  Sales
01      |   1       |    13
02      |   1       |    12       
03      |   2       |    1
04      |   2       |    4
05      |   3       |    2

我想用-1替换不存在的信息（例如产品定义->销售）。要创建查询以获取此视图，请执行以下操作：

DefID    | ProductID |  SalesID  | Sales | Column 1 | Column 2 | ....
001      |   1       |    -1     |   -1  |   text   |   text
002      |   1       |    -1     |   -1  |   text   |   text   
003      |   3       |    -1     |   -1  |   text   |   text
004      |   2       |    -1     |   -1  |   text   |   text
005      |   3       |    -1     |   -1  |   text   |   text
-1       |   1       |    01     |   13  |    -     |    -
-1       |   1       |    02     |   12  |    -     |    -       
-1       |   1       |    03     |    1  |    -     |    -  
-1       |   2       |    04     |    4  |    -     |    -  
-1       |   3       |    05     |    2  |    -     |    -  

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尝试使用

ISNULL

函数：

select ISNULL(DefID, -1) as DefID, ProductID,
       ISNULL(SalesID,-1) as SalesID, ISNULL(Sales,-1) as Sales,
       other columns...
from 

试试这个：

select DefID, ProductID, -1 as SalesID, -1 as Sales,  Column1 , Column2 
from productDefinition
union all
select -1 as DefID, ProductID,  SalesID,Sales, '-' as Column1 ,'-' as Column2 
from sales

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问题是关于连接表，而不是关于NULL