oracle with

Oracle is a technology company that specializes in database management systems, cloud services, and enterprise software. Their flagship product is the Oracle Database, which is a relational database management system that is widely used in enterprise environments. Oracle also offers a range of cloud services, including infrastructure as a service (IaaS), platform as a service (PaaS), and software as a service (SaaS). Some of the other products and services offered by Oracle include business intelligence and analytics software, customer relationship management (CRM) software, supply chain management software, and human capital management software.

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oracle with

引用\[2\]:总结：使⽤WITH AS 语句可以为⼀个⼦查询语句块定义⼀个名称，在查询语句的其他地⽅引⽤这个⼦查询。Oracle 数据库像对待内联视图或临时表⼀样对待 被引⽤的⼦查询名称，从⽽起到⼀定的优化作⽤在同级select前有多个查询定义的时候，第1个⽤with，后⾯的不⽤with，并且⽤逗号隔开。最后⼀个with ⼦句与下⾯的查询之间不能有逗号，只通过右括号分割,with ⼦句的查询必须⽤括号括起来。

问题: Oracle中的WITH语句是用来做什么的？
回答: Oracle中的WITH语句可以为一个子查询语句块定义一个名称，并在查询语句的其他地方引用这个子查询。它类似于对待内联视图或临时表一样对待被引用的子查询名称，从而起到一定的优化作用。使用WITH语句可以提高查询的可读性和性能。\[2\]
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- *1* *2* [Oracle with使用方法以及递归](https://blog.csdn.net/m0_56069948/article/details/124395684)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v91^insertT0,239^v3^insert_chatgpt"}} ] [.reference_item]
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oracle WITH

Oracle中的WITH语句也被称为子查询的公共表表达式（CTE）。它允许您在查询中创建一个命名的临时表，该表可以在查询中引用多次。WITH语句的语法如下：

WITH <subquery_name> AS (
    <subquery_definition>
)
<query_that_references_subquery_name>

其中，`<subquery_name>`是您为子查询定义的名称，`<subquery_definition>`是子查询本身，`<query_that_references_subquery_name>`是引用子查询的查询。

以下是一个使用WITH语句的示例，它使用WITH语句创建一个名为`channel_summary`的临时表，并在查询中引用它：

WITH channel_summary AS (
    SELECT channels.channel_desc, SUM(amount_sold) AS channel_total
    FROM sales, channels
    WHERE sales.channel_id = channels.channel_id
    GROUP BY channels.channel_desc
)
SELECT channel_desc, channel_total
FROM channel_summary
WHERE channel_total > (
    SELECT SUM(channel_total) * 1/3
    FROM channel_summary
);

这个查询计算每个销售渠道的销售总额，并找到销售总额超过所有渠道销售总额的1/3的渠道。在这个查询中，`channel_summary`是一个临时表，它包含了每个渠道的销售总额，可以在查询中多次引用。

使用WITH语句的好处是可以使查询更易读和易于维护。它可以将复杂的查询分解为更小的、可重用的部分，并且可以避免在查询中多次重复相同的子查询。此外，使用WITH语句还可以提高查询性能，因为它可以减少查询中的重复计算。