在in中包含null时，同正常的in，当然null in (null)除外，如下：
SQL> select 'a' from dual where 1 in(1,2,'');
'A'
---
a
SQL> select 'a' from dual where null in(1,2,'');
'A'
---
SQL> select 'a' from dual where null in(null);
'A'
---
在not in中包含null时，条件相当于永远不成立(或者unknown)，如下：
SQL> select 'a' from dual where 1 not in(1, null);
'A'
---
SQL> select 'a' from dual where 1 not in(3, null);
'A'
---
SQL> select 'a' from dual where null not in(null);
'A'
---
SQL> select 'a' from dual where null not in(null,4);
'A'
---
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