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SqlServerAS的用法 - 站长搜索
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SqlServerAS的用法

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2022-09-23 16:43:55 转载来源: 网络整理/侵权必删

SQL语句可以为表名称或列名称指定别名。(别名有时也称为导出列,不管是导出列还是别名,它们所代表的都是相同的东西

SQL语句可以为 表名称 或 列名称 指定别名。(别名有时也称为导出列,不管是导出列还是别名,它们所代表的都是相同的东西。)

SQL 别名
SQL 别名用于为 表 或 表中的列 提供临时名称。 
SQL 别名通常用于使 表名 或 列名 更具可读性。 
SQL 一个别名只存在于查询期间。 
别名使用 AS 关键字赋予。 

建议在下列情况下使用别名
查询涉及多个表 

用于查询函数

需要把两个或更多的列放在一起

列名长或可读性差

语法

1、表名的别名语法:

SELECT 列名FROM 表名 AS 别名;

2、列名的别名语法

SELECT 列名 AS 别名FROM 表名;

3、表名 和 列名 的别名混合使用语法

SELECT 列名 AS 别名FROM 表名 AS 别名;

语法举例

1、使用表名称别名

有两个表分别是:"Persons" 和 "Product_Orders"。分别为它们指定别名 "p" 和 "po"。列出 "John Adams" 的所有定单。

SELECT po.OrderID, p.LastName, p.FirstNameFROM Persons AS p, Product_Orders AS poWHERE p.LastName='Adams' AND p.FirstName='John';

2、使用列名称别名

查询 Persons 表中的 LastName 列 (为其定义别名 '姓氏')和 FirstName 列(为其定义别名 ‘名字'),输出所有结果值。

SELECT LastName AS 姓氏, FirstName AS 名字FROM Persons

3、同时使用 表名称 和 列名称

为 city 表定义别名 'A',并利用该表别名查询表中的 ID 列(为ID列定义别名 B)的所有信息。

SELECT A.ID AS BFROM city AS A;

下面是其它人的补充

1 概述

本篇文章简要分析,在SQL SERVER中,AS的基本用法

2 具体分析

2.1 定义变量类型

DECLARE @UserName AS VARCHAR(50)='Alan_beijing'

2.2 取别名

2.2.1 为结果集列取别名

code:

SELECT OrderID,CustID,OrderDate
FROM Orders

result:

code:

SELECT OrderID AS '订单ID',CustID AS '顾客ID',OrderDate AS '订单日期'
FROM Orders

result:

2.2.2  为表取别名

SELECT O.OrderID,O.CustID,O.OrderDate
FROM Orders AS O

2.2.3  为子查询取别名

SELECT ChildQuery_Orders.OrderDate
FROM
(SELECT *
FROM Orders
WHERE CustID>=5) AS ChildQuery_Orders 

2.3  转换类型

2.3.1  CAST类型转换

SELECT CAST('110' AS INT)  --110

2.3.2  CONVERT类型转换

SELECT CONVERT(decimal, '123.6') -- 123

2.4  创建视图,表示基表来源

CREATE VIEW ViewDemo
AS
SELECT * FROM Orders

2.5 其他(后续补充)

3   参考文献
【01】Microsoft  SqlServer 2008技术内幕:T-SQL 语言基础
【02】Microsoft  SqlServer 2008技术内幕:T-SQL 查询
4   版权

补充内容由Alan_beijing提供。

标签: SqlServerAS 用法


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