Chapter 4. SQL Syntax
第四章 SQL语法
This chapter describes the syntax of SQL. It forms the foundation for understanding the following
chapters which will go into detail about how SQL commands are applied to define and modify data.
该章讲述了SQL语法。为理解后面对于SQL命令如何定义和修改数据的详解章节奠定基础。
We also advise users who are already familiar with SQL to read this chapter carefully because it
contains several rules and concepts that are implemented inconsistently among SQL databases or that
are specific to PostgreSQL.
同样建议已经熟悉SQL的用户也认真的读一下本章，因为本章中包含一些与SQL数据库不一致的、独属于PostgreSQL的规则和概念等。
