Hive与Oracle表关联语句对比
在将Oracle存储过程迁移到HIVE平台时，不可避免地会遇到表关联的相应语法问题。
本文详细对比了ORALCE和HIVE的各种表关联语法，包括内关联，左，右关联，全外关联和笛卡尔积。
一.创建表
ORACLE：
create table a
(
a1 number(10),
a2 varchar2(50)
);
create table b
(
b1 number(10),
b2 varchar2(50)
);
HIVE：
CREATE TABLE IF NOT EXISTS a (
a1 STRING,
a2 STRING)
COMMENT 'TABLE A'
ROW FORMAT DELIMITED
FIELDS TERMINATED BY '|'
LINES TERMINATED BY '\n'
STORED AS TEXTFILE
TBLPROPERTIES ( 'created_at'='2014-04-28','creator'='HENRY' );
二.插入数据
ORACLE：
insert into a(a1,a2) values(1,'X');
insert into a(a1,a2) values(2,'Y');
insert into a(a1,a2) values(3,'Z');
insert into b(b1,b2) values(1,'X');
insert into b(b1,b2) values(2,'Y');
insert into b(b1,b2) values(4,'Z');
HIVE：
hive (default)> load data local inpath './data1' into table a;
Copying data from file:/home/Hadoop/roger/sql/renguihe/data
Copying file: file:/home/hadoop/roger/sql/renguihe/data
Loading data to table default.a
Table default.a stats: [num_partitions: 0, num_files: 1, num_rows: 0, total_size: 12, raw_data_size: 0]
OK
Time taken: 1.961 seconds
hive (default)> load data local inpath './data1' into table b;
Copying data from file:/home/hadoop/roger/sql/renguihe/data
Copying file: file:/home/hadoop/roger/sql/renguihe/data
Loading data to table default.b
Table default.b stats: [num_partitions: 0, num_files: 1, num_rows: 0, total_size: 12, raw_data_size: 0]
OK
Time taken: 0.392 seconds
其中data1数据文件内容为：
1|X
2|Y
3|Z
data2数据文件内容为：
1|X
2|Y
4|Z
三.等值关联
ORACLE：
select * from a,b where a.a1 = b.b1;
或：
select * from a join b on a.a1 = b.b1;
结果如下图所示：
HIVE：
select * from a join b on a.a1 = b.b1;
注意HIVE中不能使用where来表示关联条件。
执行过程及结果如下图所示：
hive (default)> select * from a join b on a.a1 = b.b1;
Total MapReduce jobs = 1
setting HADOOP_USER_NAME hadoop
Execution log at: /tmp/hadoop/.log
2014-04-29 09:13:27 Starting to launch local task to process map join; maximum memory = 1908932608
2014-04-29 09:13:27 Processing rows: 3 Hashtable size: 3 Memory usage: 110981704 rate: 0.058
2014-04-29 09:13:27 Dump the hashtable into file: file:/tmp/hadoop/hive_2014-04-29_09-13-25_273_8486588204512196396/-local-10002/HashTable-Stage-3/MapJoin-mapfile00--.hashtable
2014-04-29 09:13:27 Upload 1 File to: file:/tmp/hadoop/hive_2014-04-29_09-13-25_273_8486588204512196396/-local-10002/HashTable-Stage-3/MapJoin-mapfile00--.hashtable File size: 438
2014-04-29 09:13:27 End of local task; Time Taken: 0.339 sec.
Execution completed successfully
Mapred Local Task Succeeded . Convert the Join into MapJoin
Mapred Local Task Succeeded . Convert the Join into MapJoin
Launching Job 1 out of 1
Number of reduce tasks is set to 0 since there's no reduce operator
Starting Job = job_201404251509_0131, Tracking URL = <a href="http://IP:50030/jobdetails.jsp?jobid=job_201404251509_0131Kill" target="_blank">http://<span style="color: rgb(0, 0, 0);">IP</span>:50030/jobdetails.jsp?jobid=job_201404251509_0131
Kill</a> Command = /home/hadoop/package/hadoop-1.0.4/libexec/../bin/hadoop job -kill job_201404251509_0131
Hadoop job information for Stage-3: number of mappers: 1; number of reducers: 0
2014-04-29 09:13:39,979 Stage-3 map = 0%, reduce = 0%
2014-04-29 09:13:46,025 Stage-3 map = 100%, reduce = 0%, Cumulative CPU 1.59 sec
2014-04-29 09:13:47,034 Stage-3 map = 100%, reduce = 0%, Cumulative CPU 1.59 sec
2014-04-29 09:13:48,044 Stage-3 map = 100%, reduce = 0%, Cumulative CPU 1.59 sec
2014-04-29 09:13:49,052 Stage-3 map = 100%, reduce = 0%, Cumulative CPU 1.59 sec
2014-04-29 09:13:50,061 Stage-3 map = 100%, reduce = 0%, Cumulative CPU 1.59 sec
2014-04-29 09:13:51,069 Stage-3 map = 100%, reduce = 0%, Cumulative CPU 1.59 sec
2014-04-29 09:13:52,077 Stage-3 map = 100%, reduce = 100%, Cumulative CPU 1.59 sec
MapReduce Total cumulative CPU time: 1 seconds 590 msec
Ended Job = job_201404251509_0131
MapReduce Jobs Launched:
Job 0: Map: 1 Cumulative CPU: 1.59 sec HDFS Read: 211 HDFS Write: 16 SUCCESS
Total MapReduce CPU Time Spent: 1 seconds 590 msec
OK
a1 a2 b1 b2
1 X 1 X
2 Y 2 Y