SQL NOT

SQL NOT

SQL NOT 操作符用来对一个表达式的结果进行否定。

SQL NOT 真值表：

SELECT *
FROM TableName
WHERE NOT predicate

数据表： Employees

EmployeeId	FirstName	LastName	Department	Salary
203	Mazojys	Fxoj	Finance	78000
204	Jozzh	Lnanyo	Finance	45800
205	Syllauu	Dfaafk	Finance	57000
206	Gecrrcc	Srlkrt		62000
302	Jssme	Bdnaa	Development	75000
303	Dnnaao	Errllov	Development	55000
304	Jyoysww	Osk		49000

例1: SQL NOT　IN
选择所有LastName不是Lnanyo, Srlkrt 或 Osk 的职员(employee)：

SELECT *
FROM Employees
WHERE NOT LastName IN ('Lnanyo', 'Srlkrt', 'Osk')

我们也可以这样写：

SELECT *
FROM Employees
WHERE LastName NOT IN ('Lnanyo', 'Srlkrt', 'Osk')

结果会类似于：

EmployeeId	FirstName	LastName	Department	Salary
203	Mazojys	Fxoj	Finance	78000
205	Syllauu	Dfaafk	Finance	57000
302	Jssme	Bdnaa	Development	75000
303	Dnnaao	Errllov	Development	55000

例2: SQL NOT　LIKE
选择所有FirstName不是以”J”开始的职员(employee)：

SELECT *
FROM Employees
WHERE NOT FirstName LIKE 'J%'

我们也可以这样写：

SELECT *
FROM Employees
WHERE FirstName NOT LIKE 'J%'

结果会类似于：

EmployeeId	FirstName	LastName	Department	Salary
203	Mazojys	Fxoj	Finance	78000
205	Syllauu	Dfaafk	Finance	57000
206	Gecrrcc	Srlkrt		62000
303	Dnnaao	Errllov	Development	55000

例3: SQL IS NOT NULL
选择所有为某个部门成员的职员：

SELECT *
FROM Employees
WHERE NOT Department IS NULL

我们也可以这样写：

SELECT *
FROM Employees
WHERE Department IS NOT NULL

结果会类似于：

EmployeeId	FirstName	LastName	Department	Salary
203	Mazojys	Fxoj	Finance	78000
204	Jozzh	Lnanyo	Finance	45800
205	Syllauu	Dfaafk	Finance	57000
302	Jssme	Bdnaa	Development	75000
303	Dnnaao	Errllov	Development	55000

sqlsteps says:

2010年08月27日星期五 at 05:46上午

manner of description is good.it is also a good site to learn Sql. through this you can improve your sql skills.
life insurance says:

2010年09月14日星期二 at 10:37上午

One thing i want to know that is why NOT operator,NOT IN or NOT EXISTS had been a performance bottleneck in most of the queries? please post