将HBase中的表加载到hive中

两种方式加载hbase中的表到hive中，一是hive创建外部表关联hbase表数据，二是hive创建普通表将hbase的数据加载到本地

1. 创建外部表

hbase中已经有了一个test表，内容如下

hbase(main):012:0* scan 'test'
ROW                                 COLUMN+CELL
 001                                column=info:age, timestamp=1526563694645, value=18
 001                                column=info:name, timestamp=1526563629119, value=tom
 002                                column=info:age, timestamp=1526563723288, value=19
 002                                column=info:name, timestamp=1526563706773, value=jerry
2 row(s) in 0.4320 seconds

接下来我们创建一个hive的外部表

CREATE EXTERNAL TABLE test_external (key int, name string,age int)
STORED BY 'org.apache.hadoop.hive.hbase.HBaseStorageHandler'
WITH SERDEPROPERTIES ("hbase.columns.mapping" = ":key,info:name,info:age")
TBLPROPERTIES ("hbase.table.name" = "test");

注：EXTERNAL 关键字指定创建一个外部表

进入hive shell，执行上面的建表语句

hive> CREATE EXTERNAL TABLE test_external (key int, name string,age int)
    > STORED BY 'org.apache.hadoop.hive.hbase.HBaseStorageHandler'
    > WITH SERDEPROPERTIES ("hbase.columns.mapping" = ":key,info:name,info:age")
    > TBLPROPERTIES ("hbase.table.name" = "test");
OK
Time taken: 0.331 seconds

hive可以使用类sql语句执行查询命令

hive> select * from test_external;
OK
1       tom     18
2       jerry   19
Time taken: 0.313 seconds, Fetched: 2 row(s)

2. 创建普通表

hive外部表，仅记录数据所在的路径， 不对数据的位置做任何改变。在删除表的时候，内部表的元数据和数据会被一起删除， 而外部表只删除元数据，不删除数据。接下来我们创建普通表（内部表），并将hbase表数据加载到内部表中。

hive> create table test (key string, name string,age string)
    > ROW FORMAT DELIMITED FIELDS TERMINATED BY '\t'
    > STORED AS TEXTFILE;
OK
Time taken: 0.154 seconds

执行sql命令INSERT OVERWRITE TABLE test SELECT * FROM test_external，通过外部表将hbase中的表数据加载到hive本地表

hive> INSERT OVERWRITE TABLE test SELECT * FROM test_external;
Query ID = hadoop_20180519102929_b52c1820-7d93-4baf-a410-8604bfd0e43b
Total jobs = 3
Launching Job 1 out of 3
Number of reduce tasks is set to 0 since there's no reduce operator
Starting Job = job_1525962191655_0030, Tracking URL = http://SHQZ-PS-IOT-TEST-WEB01:8088/proxy/application_1525962191655_0030/
Kill Command = /opt/cloudera/parcels/CDH-5.8.4-1.cdh5.8.4.p0.5/lib/hadoop/bin/hadoop job  -kill job_1525962191655_0030
Hadoop job information for Stage-1: number of mappers: 1; number of reducers: 0
2018-05-19 10:30:18,571 Stage-1 map = 0%,  reduce = 0%
2018-05-19 10:30:31,505 Stage-1 map = 100%,  reduce = 0%, Cumulative CPU 4.68 sec
MapReduce Total cumulative CPU time: 4 seconds 680 msec
Ended Job = job_1525962191655_0030
Stage-4 is selected by condition resolver.
Stage-3 is filtered out by condition resolver.
Stage-5 is filtered out by condition resolver.
Moving data to: hdfs://nameservice1/user/hive/warehouse/test/.hive-staging_hive_2018-05-19_10-29-59_285_1972684120193290878-1/-ext-10000
Loading data to table default.test
Table default.test stats: [numFiles=1, numRows=2, totalSize=20, rawDataSize=18]
MapReduce Jobs Launched:
Stage-Stage-1: Map: 1   Cumulative CPU: 4.68 sec   HDFS Read: 3811 HDFS Write: 88 SUCCESS
Total MapReduce CPU Time Spent: 4 seconds 680 msec
OK
Time taken: 34.13 seconds

加载hbase表数据到hive内部表中，是通过启动一个mapreduce任务来进行的；另外hive的sql基本上都是转换成mapreduce任务来执行。

hive> select * from test;
OK
1       tom     18
2       jerry   19
Time taken: 0.194 seconds, Fetched: 2 row(s)