如果计算结果为负，则显示 NULL，如何解决此问题？

Question

所以我正在验证源表和目标表之间的计数，如果计数不同，它可以是正数或负数，但是当是负数时它会显示 NULL。我曾经知道这一点，但在我看来，我的记忆力很差。我的代码如下。

with cte as (
            select 'source' [object],count(contract_id) as total_count
            FROM [account].[dbo].[account] act
            left join [account].[dbo].[contract] cont
            on act.account_id = cont.account_id)
,cte1 as(
          select 'target' [object], count(contract_id) as total_count
          from [account].[dbo].[action]
          union
          select * from cte)
          select * from cte1 
          union
          select 'diff' [object],
                 (select total_count from cte where [object] = 'source')
                -
                 (select total_count from cte where [object] = 'target')  

结果如下 object total_count target 28402 source 28401 diff NULL -- 这里应该是负 1 (-1)

Answer 1

问题在这里：

（从 cte 中选择 total_count 其中 [object] = 'target'）

“cte” cte 中没有 object = 'target'。
由于select返回null，计算也必须返回null。

试试这个：（将 cte 更改为 cte1）

with cte as (
            select 'source' [object],count(contract_id) as total_count
            FROM [account].[dbo].[account] act
            left join [account].[dbo].[contract] cont
            on act.account_id = cont.account_id)
,cte1 as(
          select 'target' [object], count(contract_id) as total_count
          from [account].[dbo].[action]
          union
          select * from cte)
          select * from cte1 
          union
          select 'diff' [object],
                 (select total_count from cte where [object] = 'source')
                -
                 (select total_count from cte1 where [object] = 'target')