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文章 2017-12-12 来自：开发者社区

PostgreSQL在何处处理 sql查询之十

回到 exec_simple_query函数上来。 /* * exec_simple_query * * Execute a "simple Query" protocol message. */ static void exec_simple_query(const char *query_string) { ... start_xact_command(); ...

文章 2017-12-12 来自：开发者社区

PostgreSQL在何处处理 sql查询之十九

再回过头来看 /* * open a file in an arbitrary directory * * NB: if the passed pathname is relative (which it usually is), * it will be interpreted relative to the process' working directory * (whic...

文章 2017-12-12 来自：开发者社区

PostgreSQL在何处处理 sql查询之二十四

接前面，回到 get_relation_info(plancat.c)函数上： relation 是由 heap_open 函数调用后获得的。 void get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent, RelOptInfo *rel) { Ind...

文章 2017-12-12 来自：开发者社区

PostgreSQL在何处处理 sql查询之四十八

接着，分析： /*-------------------- * subquery_planner * Invokes the planner on a subquery. We recurse to here for each * sub-SELECT found in the query tree. * * glob is the global state ...

文章 2017-12-05 来自：开发者社区

PostgreSQL在何处处理 sql查询之二十五

再次梳理 build_simple_rel 的执行内容： /* * build_simple_rel * Construct a new RelOptInfo for a base relation or 'other' relation. */ RelOptInfo * build_simple_rel(PlannerInfo *root, int relid, RelO...

文章 2017-08-18 来自：开发者社区

PostgreSQL SQL 语言：索引

本文档为PostgreSQL 9.6.0文档，本转载已得到原译者彭煜玮授权。 1. 简介假设我们有一个如下的表： CREATE TABLE test1 ( id integer, content varchar ); 而应用发出很多以下形式的查询： SELECT content FROM test1 WHERE id = constant; 在没有事前准备的情况下，系统不得...

文章 2017-08-18 来自：开发者社区

本文档为PostgreSQL 9.6.0文档，本转载已得到原译者彭煜玮授权。 1. 概述 SQL是一种强类型语言。也就是说，每个数据项都有一个相关的数据类型，数据类型决定其行为和允许的用法。 PostgreSQL有一个可扩展的类型系统，该系统比其它SQL实现更具通用和灵活。因而，PostgreSQL中大多数类型转换行为是由通用规则来管理的，而不是ad hoc启发式规则。这种做法允许使用混合类型表....

文章 2017-08-17 来自：开发者社区

PostgreSQL SQL 语言：数据类型

本文档为PostgreSQL 9.6.0文档，本转载已得到原译者彭煜玮授权。 1. 数字类型数字类型由2、4或8字节的整数以及4或8字节的浮点数和可选精度小数组成。Table 8-2列出了所有可用类型。 Table 8-2. 数字类型下面的几节详细描述这些类型。 1.1. 整数类型类型smallint、integer和bigint存储各种范围的全部是数字的数，也就是没有小数部分的数字。试.....

文章 2017-08-16 来自：开发者社区

PostgreSQL SQL 语言：数据定义

本文档为PostgreSQL 9.6.0文档，本转载已得到原译者彭煜玮授权。 1.表基础关系型数据库中的一个表非常像纸上的一张表：它由行和列组成。列的数量和顺序是固定的，并且每一列拥有一个名字。行的数目是变化的，它反映了在一个给定时刻表中存储的数据量。SQL并不保证表中行的顺序。当一个表被读取时，表中的行将以非特定顺序出现，除非明确地指定需要排序。这些将在Chapter 7介绍。此外，SQL不....

文章 2017-08-16 来自：开发者社区

PostgreSQL教程（二）：SQL语言

本文档为PostgreSQL 9.6.0文档，本转载已得到原译者彭煜玮授权。 2.1. 引言本章提供一个如何使用SQL执行简单操作的概述。本教程的目的只是给你一个介绍，并非完整的SQL教程。有许多关于SQL的书籍，包括Understanding the New SQL和A Guide to the SQL Standard。你还要知道有些PostgreSQL语言特性是对标准的扩展。在随后的例....

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