SQL WHERE

SQL WHERE 子句用来过滤查询结果，可以用于 SQL Select, update, delete, insert 等语句。

SELECT *
FROM 表名
WHERE ColumnName operator Value

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	Finance	62000
302	Jssme	Bdnaa	Development	75000
303	Dnnaao	Errllov	Development	55000
304	Tyoysww	Osk	Development	49000

下面是不同操作符的例子：

= (等于)

SELECT *
FROM Employees
WHERE FirstName = 'Jssme'

<> (不等于)

SELECT *
FROM Employees
WHERE FirstName <> 'Jssme'

> (大于)

SELECT *
FROM Employees
WHERE Salary > 55000

< (小于)

SELECT *
FROM Employees
WHERE Salary < 55000

>= (大于或等于)

SELECT *
FROM Employees
WHERE Salary >= 55000

<= (小于或等于)

SELECT *
FROM Employees
WHERE Salary <= 55000

BETWEEN (在一个范围之间)

SELECT *
FROM Employees
WHERE Salary BETWEEN 55000 AND 75000

LIKE (模糊查询)

SELECT *
FROM Employees
WHERE FirstName LIKE 'Jss%'

IN (在一个数据集中)

SELECT *
FROM Employees
WHERE EmployeeId IN (203, 204, 302)

我们也可以将这些操作符联在一起：

SELECT *
FROM Employees
WHERE (FirstName LIKE 'J%'
       AND Salary > 55000
      )
      OR EmployeeId = 304