逻辑条件将两个组成条件的结果组合在一起，从而基于它们产生单个结果，或者反转单个条件的结果。
1、NOT
如果条件为FALSE，则返回TRUE。
如果条件为TRUE，则返回FALSE。
SELECT *
FROM employees
WHERE NOT
(salary BETWEEN 1000 AND 2000)
ORDER BY employee_id;
SELECT *
FROM employees
WHERE NOT (job_id IS NULL)
ORDER BY employee_id;
2、AND
如果两个条件都为TRUE，则返回TRUE。
如果其中一个条件为FALSE，则为FALSE。
SELECT *
FROM employees
WHERE job_id = 'PU_CLERK'
AND department_id = 30
ORDER BY employee_id;
3、OR
如果其中一个条件为TRUE，则返回TRUE。
如果两个条件都为FALSE，则返回FALSE。
SELECT *
FROM employees
WHERE job_id = 'PU_CLERK'
OR department_id = 10
ORDER BY employee_id;
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--and,or,not
SELECT * FROM emp WHERE SAL > 800 OR SAL < 3000;
SELECT * FROM emp WHERE SAL > 800 AND SAL < 3000;
SELECT * FROM emp WHERE NOT SAL < 3000;
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