Sql語言的概念包含3部分內容。sql的歷史，以及各個版本的歷史，Sql標準的組成部分，Sql語句的分類。
1、版本
SQL-87：Standard first formalized by ANSI; support for transactions and CREATE, READ, UPDATE, and DELETE operations
標準的新增，查詢，更新，刪除操作。
SQL-89：Minor revision, added referential integrity constraints
完整性約束。
SQL-92：Major revision (ISO 9075), added support for internationalization, etc.
增加國際化。
SQL-1999：Added support for user-defined types, regular expression mapping, triggers, procedural and control-flow statements, and more
增加用戶自定義類型，正則表達式，觸發器，procedural和流程控制語句等。
SQL-2003：Added support for XML and OLAP (window functions), sampling, and enhanced numeric functions
支持XML和OLAP, 增強數字函數
SQL-2006：Clarified how SQL and SML interact and added support for XQuery
支持Xquery
SQL-2008：Incorporated various improvements and enhancements that had been made in several of the most prominent RDBMS platforms (INSTEAD OF triggers, TRUNCATE statement, FETCH clause, etc.) and expanded the XML specification
對原有的一些對象進行增強
SQL-2011: Introduced new features for managing temporal data
管理臨時數據增加新功能。
SQL-2016：Described how SQL interacts with JavaScript Object Notation (JSON) and added support for polymorphic table functions and row pattern matching
增加Json的支持。
SQL-2019：Described how SQL interacts with multidimensional arrays (MDAs)
增加多維數組。
2、組成部分
SQL/Framework：
SQL/Foundation：
SQL/CLI (Call-Level Interface)：從其他編程語言動態執行sql
SQL/PSM (Persistent Stored Modules)
SQL/MED (Management of External Data)
SQL/OLB (Object Language Binding)：與面嚮對象語言綁定，例如JDBC
SQL/Schemata：元信息
SQL/JRT (Java Routines and Types)：
SQL/XML：添加XML數據類型，並實現相關的操作。
3、語句分類
