The meaning of as in sql

AS is used as a keyword in SQL to assign names to aliases or temporary tables to improve query readability and understandability. Uses include: creating aliases for tables or columns; creating temporary tables for derived tables or views.

AS meaning in SQL

Meaning

AS Is a keyword in SQL used to assign a name to an alias or temporary table. It allows us to refer to tables, columns or expressions by different names, thus improving the readability and understandability of queries.

Uses

AS is mainly used for the following purposes:

• Create aliases for tables or columns:This can Simplify long table or column names or rename them to something more descriptive. For example:

SELECT * FROM users AS u

• Create a temporary table for a derived table or view: When assigning query results to a temporary table, you can use AS to name the table. For example:

SELECT * FROM users
WHERE age > 30
AS old_users

Syntax

The syntax for using AS is as follows:

[对象名称] AS [别名]

Among them:

• [Object Name] is the table, column, or expression for which you want to create an alias.
• [alias] is the name to be assigned to the object.

Examples

Here are some examples using AS:

-- 为 users 表创建别名 u
SELECT * FROM users AS u

-- 为派生表创建临时表 old_users
SELECT * FROM users
WHERE age > 30
AS old_users

-- 为计算列 age_group 创建别名 group
SELECT *,
    CASE
        WHEN age < 18 THEN 'Child'
        WHEN age < 65 THEN 'Adult'
        ELSE 'Senior'
    END AS age_group
FROM users

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