Sql 最简单的形式，逻辑定律如下，给出两个命题P1和P2： 非（P1和P2）=>（非P1或非P2） 非（P1或P2）=>（非P1和P2）

请注意，这些也是正确的：

• （P1和P2）

  =>

  非（非P1或非P2）

• （P1或P2）

  =>

  非（非P1和非P2）

---

这些转换也非常有用。

这个概念适用于数学和逻辑，严格来说不是编码。这只是逻辑上的方式和/或工作方式

这个概念适用于数学和逻辑，并不是严格意义上的编码。这只是逻辑上的方式和/或工作方式

你知道布尔

或
运算符是如何工作的吗？我想你需要（dept='Marketing）和（job'Sam-Wise'）以及（job'the-Precious'）你知道布尔
或
运算符是如何工作的吗？我想你需要（dept='Marketing）和（job'Sam-Wise'）以及（job'the-preciouse'））对数字逻辑101和101的倒叙。停止疯狂@user92546谢谢你的名字！我只是从经验中直觉地知道了这条定律。+1值得注意的是，尽管SQL有三值逻辑，但De Morgan定律在SQL中仍然成立。数字逻辑101和101的倒叙。停止疯狂@user92546谢谢你的名字！我只是从经验中直觉地知道了这条定律。+1值得注意的是，尽管SQL有三值逻辑，但De Morgan定律在SQL中仍然成立。
select dept, job
from organizations
where (dept = 'Marketing' and job <> 'Sam Wise')
or    (dept = 'Marketing' and job <> 'The Precious')

select dept, job
from organizations
where (dept = 'Marketing' and job <> 'Sam Wise')
and   (dept = 'Marketing' and job <> 'The Precious')

WHERE dept = 'Marketing' AND job NOT IN ('Sam Wise', 'The Precious');

SELECT dept, job
FROM organizations
WHERE
   dept = 'Marketing'
   and job <> 'Sam Wise'
   and job <> 'The Precious'

where (dept = 'Marketing' and job <> 'Sam Wise')
or    (dept = 'Marketing' and job <> 'The Precious')

statement1 = true OR statemet2 = true ...result true
statement1 = false OR statemet2 = true ...result true
statement1 = true OR statemet2 = false...result true
statement1 = false OR statemet2 = false ...result false

statement1 = true AND statemet2 = true ...result true
statement1 = false AND statemet2 = true ...result false
statement1 = true AND statemet2 = false...result false
statement1 = false AND statemet2 = false ...result false

(dept = 'Marketing' and 'Sam Wise' <> 'Sam Wise') -- FALSE
OR    
(dept = 'Marketing' and 'Sam Wise' <> 'The Precious') -- TRUE

(dept = 'Marketing' and job <> 'Sam Wise') 
OR (dept = 'Marketing' and job <> 'The Precious')

(TRUE and FALSE) 
OR (TRUE and TRUE)

(FALSE)
OR (TRUE)

(TRUE)

select dept, job
from organizations
where
   dept = 'Marketing'
   and not (
      job = 'Sam Wise'
      or job = 'The Precious'
   )

select dept, job
from organizations
where
   dept = 'Marketing'
   and job <> 'Sam Wise'
   and job <> 'The Precious'

select dept, job
from organizations
where
   dept = 'Marketing'
   and job not in ('Sam Wise', 'The Precious')