hive中的join

建表

: jdbc:hive2://localhost:10000> create database myjoin;
No rows affected (3.78 seconds)
: jdbc:hive2://localhost:10000> use myjoin;
No rows affected (0.419 seconds)
: jdbc:hive2://localhost:10000> create table a(id int,name string) row format delimited fields terminated by ',';
No rows affected (2.08 seconds)
: jdbc:hive2://localhost:10000> create table b(id int,name string) row format delimited fields terminated by ',';

: jdbc:hive2://localhost:10000> select * from a
: jdbc:hive2://localhost:10000> ;
+-------+---------+--+
| a.id  | a.name  |
+-------+---------+--+
|      | qq      |
|      | ww      |
|      | ee      |
|      | rr      |
|      | tt      |
|      | yy      |
|      | aa      |
|      | ss      |
|     | zz      |
+-------+---------+--+
 rows selected (1.881 seconds)
: jdbc:hive2://localhost:10000> select * from b;
+-------+---------+--+
| b.id  | b.name  |
+-------+---------+--+
|      | qq      |
|      |       |
|      | dd      |
|      | rr      |
|      | fgf     |
|      | as      |
|      |       |
|     | ww      |
|     |        |
|     |       |
|     |       |
|     | 4r      |
+-------+---------+--+
 rows selected (0.147 seconds)

inner join 的结果，也就是join
0: jdbc:hive2://localhost:10000> select a.*,b.* from a inner join b on a.id = b.id;
INFO  : Execution completed successfully
INFO  : MapredLocal task succeeded
INFO  : Number of reduce tasks is set to  since there's no reduce operator
INFO  : number of splits:
INFO  : Submitting tokens for job: job_1496277833427_0007
INFO  : The url to track the job: http://mini2:8088/proxy/application_1496277833427_0007/
INFO  : Starting Job = job_1496277833427_0007, Tracking URL = http://mini2:8088/proxy/application_1496277833427_0007/
INFO  : Kill Command = /home/hadoop/xxxxxx/hadoop265/bin/hadoop job  -kill job_1496277833427_0007
INFO  : Hadoop job information for Stage-: number of mappers: ; number of reducers:
INFO  : -- ::, Stage- map = %,  reduce = %
INFO  : -- ::, Stage- map = %,  reduce = %, Cumulative CPU 5.05 sec
INFO  : MapReduce Total cumulative CPU time:  seconds  msec
INFO  : Ended Job = job_1496277833427_0007
+-------+---------+-------+---------+--+
| a.id  | a.name  | b.id  | b.name  |
+-------+---------+-------+---------+--+
|      | qq      |      | qq      |
|      | ww      |      |       |
|      | ee      |      | dd      |
|      | rr      |      | rr      |
|      | yy      |      | fgf     |
|      | aa      |      | as      |
+-------+---------+-------+---------+--+

full outer join ，两边的数据都会出来只不过on条件没有对应上的一端会显示为null

: jdbc:hive2://localhost:10000> select a.*,b.* from a full outer join b on a.id = b.id;
INFO  : Number of reduce tasks not specified. Estimated from input data size:
INFO  : In order to change the average load for a reducer (in bytes):
INFO  :   set hive.exec.reducers.bytes.per.reducer=<number>
INFO  : In order to limit the maximum number of reducers:
INFO  :   set hive.exec.reducers.max=<number>
INFO  : In order to set a constant number of reducers:
INFO  :   set mapreduce.job.reduces=<number>
INFO  : number of splits:
INFO  : Submitting tokens for job: job_1496277833427_0008
INFO  : The url to track the job: http://mini2:8088/proxy/application_1496277833427_0008/
INFO  : Starting Job = job_1496277833427_0008, Tracking URL = http://mini2:8088/proxy/application_1496277833427_0008/
INFO  : Kill Command = /home/hadoop/xxxxxx/hadoop265/bin/hadoop job  -kill job_1496277833427_0008
INFO  : Hadoop job information for Stage-: number of mappers: ; number of reducers:
INFO  : -- ::, Stage- map = %,  reduce = %
INFO  : -- ::, Stage- map = %,  reduce = %
INFO  : -- ::, Stage- map = %,  reduce = %
INFO  : -- ::, Stage- map = %,  reduce = %, Cumulative CPU 6.52 sec
INFO  : -- ::, Stage- map = %,  reduce = %, Cumulative CPU 9.17 sec
INFO  : -- ::, Stage- map = %,  reduce = %, Cumulative CPU 12.65 sec
INFO  : MapReduce Total cumulative CPU time:  seconds  msec
INFO  : Ended Job = job_1496277833427_0008
+-------+---------+-------+---------+--+
| a.id  | a.name  | b.id  | b.name  |
+-------+---------+-------+---------+--+
|      | qq      |      | qq      |
|      | ww      |      |       |
|      | ee      |      | dd      |
|      | rr      |      | rr      |
|      | tt      | NULL  | NULL    |
|      | yy      |      | fgf     |
|      | aa      |      | as      |
|      | ss      | NULL  | NULL    |
| NULL  | NULL    |      |       |
|     | zz      | NULL  | NULL    |
| NULL  | NULL    |     |       |
| NULL  | NULL    |     | ww      |
| NULL  | NULL    |     |       |
| NULL  | NULL    |     | 4r      |
| NULL  | NULL    |     |        |
+-------+---------+-------+---------+--+
 rows selected (371.304 seconds)

select a.*from a left semi join b on a.id = b.id; -- from 前不能写b.* 否则会报错（ Error while compiling statement: FAILED: SemanticException [Error 10009]: Line 1:11 Invalid table alias 'b' (state=42000,code=10009)）

替代exist in 的用法，返回值只是inner join 中左边的一般，

+-------+---------+--+
| a.id  | a.name  |
+-------+---------+--+
|      | qq      |
|      | ww      |
|      | ee      |
|      | rr      |
|      | yy      |
|      | aa      |
+-------+---------+--+

没有 right semi join

left semi join 是exist in 的高效实现，比inner join 效率高