HIVE Indexex 索引

问题导读

1、Hive可以创建哪些索引？
2、Hive如何创建分区索引、唯一性索引？



Creating an Index -- 创建一个索引
[sql]

CREATE TABLE employees (  
  name         STRING,  
  salary       FLOAT,  
  subordinates ARRAY<STRING>,  
  deductions   MAP<STRING, FLOAT>,  
  address      STRUCT<street:STRING, city:STRING, state:STRING, zip:INT>  
)  
PARTITIONED BY (country STRING, state STRING);
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Let’s index on the country partition only:（让我们唯一分区索引）
[sql]

CREATE INDEX employees_index  
ON TABLE employees (country)  
AS 'org.apache.hadoop.hive.ql.index.compact.CompactIndexHandler'  
WITH DEFERRED REBUILD  
IDXPROPERTIES ('creator = 'me', 'created_at' = 'some_time')  
IN TABLE employees_index_table  
PARTITIONED BY (country, name)  
COMMENT 'Employees indexed by country and name.';  
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Bitmap Indexes
Hive v0.8.0 adds a built-in bitmap index handler. Bitmap indexes are commonly used
for columns with few distinct values. Here is our previous example rewritten to use the
bitmap index handler:
（Hive 0.8.0添加了一个内置的位图索引处理程序。位图索引是常用的具有几个不同值的列。这是我们的前一个例子重写使用，位图索引处理程序:）
[sql]

CREATE INDEX employees_index  
ON TABLE employees (country)  
AS 'BITMAP'  
WITH DEFERRED REBUILD  
IDXPROPERTIES ('creator = 'me', 'created_at' = 'some_time')  
IN TABLE employees_index_table  
PARTITIONED BY (country, name)  
COMMENT 'Employees indexed by country and name.'; 
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Rebuilding the Index
（重建索引）
[sql]

ALTER INDEX employees_index  
ON TABLE employees  
PARTITION (country = 'US')  
REBUILD;  
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Showing an Index
（查看索引）
[sql]

SHOW FORMATTED INDEX ON employees;  
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Dropping an Index
（删除索引）
[sql]

DROP INDEX IF EXISTS employees_index ON TABLE employees;
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IN TABLE employees_index_table    这句是表达啥意思呢？

内置的位图索引处理程序

创建索引有什么意义呢？对性能没影响吧