PostgreSQL Oracle PL/SQL 兼容性之 - AGGREGATE USING Clause 聚合函数

最新推荐文章于 2021-04-12 08:45:29 发布

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最新推荐文章于 2021-04-12 08:45:29 发布

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文章标签：数据库

原文链接：https://yq.aliyun.com/articles/603286

版权

这篇博客探讨了PostgreSQL如何实现与Oracle中AGGREGATE USING Clause类似的聚合函数功能。文章介绍了Oracle的AGGREGATE USING Clause，自定义聚合函数的限制以及在PostgreSQL中创建和使用自定义聚合函数的方法，包括并行聚合函数的实现。还提供了一些示例和相关资源链接。

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背景

Oracle的自定义聚合函数的定义方法，在创建函数是，使用AGGREGATE USING Clause关键词。

AGGREGATE USING Clause

Specify AGGREGATE USING to identify this function as an aggregate function, or one that evaluates a group of rows and returns a single row. You can specify aggregate functions in the select list, HAVING clause, and ORDER BY clause.

When you specify a user-defined aggregate function in a query, you can treat it as an analytic function (one that operates on a query result set). To do so, use the OVER analytic_clause syntax available for built-in analytic functions. See "Analytic Functions" for syntax and semantics.

In the USING clause, specify the name of the implementation type of the function. The implementation type must be an object type containing the implementation of the ODCIAggregate routines. If you do not specify schema, Oracle Database assumes that the implementation type is in your own schema.

Restriction on Creating Aggregate Functions
If you specify this clause, you can specify only one input argument for the function.

自定义的聚合函数，与普通聚合函数一样，可以用于聚合、KEEP等操作SQL中。