Shulou(Shulou.com)06/01 Report--

The SQL statement can specify an alias for a table name or column name. Aliases are sometimes called export columns, and whether they are export columns or aliases, they all represent the same thing. )

SQL alias

SQL aliases are used to provide temporary names for a table or a column in a table.

SQL aliases are commonly used to make table or column names more readable.

An alias for SQL exists only during the query.

Aliases are given using the AS keyword.

Aliases are recommended in the following situations

The query involves multiple tables

Used to query functions

Two or more columns need to be put together

Long list or poor readability

Grammar

1. Alias syntax for table names:

SELECT column name FROM table name AS alias

2. Alias syntax for column names

SELECT column name AS alias FROM table name

3. Mixed syntax for aliases of table and column names

SELECT column name AS alias FROM table name AS alias

Grammar examples

1. Use the table name to alias

There are two tables: "Persons" and "Product_Orders". Assign them aliases "p" and "po", respectively. List all orders for "John Adams".

SELECT po.OrderID, p.LastName, p.FirstNameFROM Persons AS p, Product_Orders AS poWHERE p.LastNameplates Adams' AND p.FirstNameplates John'

2. Use column name aliases

Query the LastName column in the Persons table (define the alias' last name 'for it) and the FirstName column (define the alias' first name 'for it), and output all the result values.

SELECT LastName AS last name, FirstName AS first name FROM Persons

3. Use both table and column names

Define the alias' alias' for the city table and use that table alias to query all information about the ID column in the table (alias B is defined for the ID column).

SELECT A.ID AS BFROM city AS A

Here are some additions from others

1 Overview

This article briefly analyzes the basic usage of AS in SQL SERVER.

2 concrete analysis

2.1 define variable types

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

2.2 aliases

2.2.1 alias the result set column

Code:

SELECT OrderID,CustID,OrderDate

FROM Orders

Result:

Code:

SELECT OrderID AS 'order ID',CustID AS' customer ID',OrderDate AS 'order date'

FROM Orders

Result:

2.2.2 alias the table

SELECT O.OrderID,O.CustID,O.OrderDate

FROM Orders AS O

2.2.3 alias for subquery

SELECT ChildQuery_Orders.OrderDate

FROM

(SELECT *

FROM Orders

WHERE CustID > = 5) AS ChildQuery_Orders

2.3 conversion types

2.3.1 CAST type conversion

SELECT CAST ('110' AS INT)-

2.3.2 CONVERT type conversion

SELECT CONVERT (decimal, '123.6')-123

2.4 create a view that represents the source of the base table

CREATE VIEW ViewDemo

AS

SELECT * FROM Orders

2.5 others (follow-up additions)

3 references

[01] Microsoft SqlServer 2008 Technical Insider: T-SQL language Foundation

[02] Microsoft SqlServer 2008 technical insider: T-SQL query

4 copyright

The supplementary content is provided by Alan_beijing.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.