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一、前言
DDL,也叫数据定义语言 (Data Definition Language,
DDL),是SQL语言集中对数据库内部的对象结构进行创建,删除,修改等的操作语言,这些数据库对象包括database、table等,使用过mysql的同学应该对此很了解了;
hive中ddl核心操作
* 核心语法由CREATE、ALTER与DROP三个所组成;
* DDL不涉及表内部数据的操作;
二、Hive中DDL语法特点
Hive SQL(HQL)与标准SQL的语法大同小异,基本相通,使用过标准sql的同学上手hive
sql时基本无压力,但hive的复杂查询语法相对标准sql来说,细节上又略有不同,后续在实操中可以发现;
HQL中create语法(尤其create table)将是学习掌握Hive
DDL语法的重中之重,建表是否成功直接影响数据文件是否映射成功,进而影响后续是否可以基于SQL分析数据
三、Hive中的database
数据库是数据表的基本承载体,现有数据库才会有表,Hive中的数据库有下面的特点
1、默认数据库为default
存储数据位置位于HDFS的/user/hive/warehouse下;