分桶表
将数据按照指定的字段进行分成多个桶中去,说白了就是将数据按照字段进行划分,可以将数据按照字段划分到多个文件当中去
开启hive的桶表功能
set hive.enforce.bucketing=true;
设置reduce的个数
set mapreduce.job.reduces=3;
创建桶表
create table course (c_id string,c_name string,t_id string) clustered by(c_id) into 3 buckets row format delimited fields terminated by '\t';
桶表的数据加载,由于桶表的数据加载通过hdfs dfs -put文件或者通过load data均不好使,只能通过insert overwrite
创建普通表,并通过insert overwrite的方式将普通表的数据通过查询的方式加载到桶表当中去
创建普通表:
create table course_common (c_id string,c_name string,t_id string) row format delimited fields terminated by '\t';
普通表中加载数据
load data local inpath '/export/servers/hivedatas/course.csv' into table course_common;
通过insert overwrite给桶表中加载数据
insert overwrite table course select * from course_common cluster by(c_id);
修改表
表重命名
基本语法:
alter table old_table_name rename to new_table_name;
把表score4修改成score5
alter table score4 rename to score5;
增加/修改列信息
(1)查询表结构
desc score5;
(2)添加列
alter table score5 add columns (mycol string, mysco string);
(3)查询表结构
desc score5;
(4)更新列
alter table score5 change column mysco mysconew int;
(5)查询表结构
desc score5;
删除表
drop table score5;
hive表中加载数据
直接向分区表中插入数据
create table score3 like score;
insert into table score3 partition(month ='201807') values ('001','002','100'); (一般不这么做,插入一条数据就会增加一个小文件)
通过查询插入数据(掌握)
通过load方式加载数据
load data local inpath '/export/servers/hivedatas/score.csv' overwrite into table score partition(month='201806');
通过查询方式加载数据
create table score4 like score;
insert overwrite table score4 partition(month = '201806') select s_id,c_id,s_score from score;
{注意:
1.此处不能使用select * from score,否则报错:Error: Error while compiling statement: FAILED: SemanticException [Error 10044]: Line 1:23 Cannot insert into target table because column number/types are different ''201902'': Table insclause-0 has 3 columns, but query has 4 columns. (state=42000,code=10044)
2.关键字overwrite 必须要有
}
多插入模式(用得不多)
常用于实际生产环境当中,将一张表拆开成两部分或者多部分
给score表加载数据
load data local inpath '/export/servers/hivedatas/score.csv' overwrite into table score partition(month='201806');
创建第一部分表:
create table score_first( s_id string,c_id string) partitioned by (month string) row format delimited fields terminated by '\t' ;
创建第二部分表:
create table score_second(c_id string,s_score int) partitioned by (month string) row format delimited fields terminated by '\t';
分别给第一部分与第二部分表加载数据
from score insert overwrite table score_first partition(month='201806') select s_id,c_id insert overwrite table score_second partition(month = '201806') select c_id,s_score;
查询语句中创建表并加载数据(as select)
将查询的结果保存到一张表当中去
create table score5 as select * from score;
创建表时通过location指定加载数据路径
1)创建表,并指定在hdfs上的位置
create external table score6 (s_id string,c_id string,s_score int) row format delimited fields terminated by '\t' location '/myscore6';
2)上传数据到hdfs上
hdfs dfs -mkdir -p /myscore6
hdfs dfs -put score.csv /myscore6;
3)查询数据
select * from score6;
export导出与import 导入 hive表数据(内部表操作)
create table techer2 like techer;
export table techer to '/export/techer';
import table techer2 from '/export/techer';
hive表中的数据导出(了解)
将hive表中的数据导出到其他任意目录,例如linux本地磁盘,例如hdfs,例如mysql等等
insert导出
1)将查询的结果导出到本地
insert overwrite local directory '/export/servers/exporthive' select * from score;
2)将查询的结果格式化导出到本地
insert overwrite local directory '/export/servers/exporthive' row format delimited fields terminated by '\t' collection items terminated by '#' select * from student;
3)将查询的结果导出到HDFS上(没有local)
insert overwrite directory '/export/servers/exporthive' row format delimited fields terminated by '\t' collection items terminated by[a1] '#' select * from score;
(对于集合类型我们使用#来进行分割,因为这个表里面没有集合类型,所以加不加这个结果都一样)
Hadoop命令导出到本地
dfs -get /export/servers/exporthive/000000_0 /export/servers/exporthive/local.txt;
hive shell 命令导出
基本语法:(hive -f/-e 执行语句或者脚本 > file)
bin/hive -e "select * from myhive.score;" > /export/servers/exporthive/score.txt
export导出到HDFS上
export table score to '/export/exporthive/score';
sqoop导出
后续单独讲。
清空表数据
只能清空管理表,也就是内部表
truncate table score6;
清空外部表会报错(
Error: Error while compiling statement: FAILED: SemanticException [Error 10146]: Cannot truncate non-managed table score5. (state=42000,code=10146)
)