hive使用过的基本命令

命令：完成操作

hive：进去hive

show databases：显示 所有database

use wizad： 使用database wizad，或者如use aso

show tables：显示当前database下的所有表

show columns from table_name from database_name; 或show columns from database_name.table_name; ：显示表中列名称

show grants for user_name@localhost;：显示一个用户的权限，显示结果类似于grant 命令

show index from table_name;：显示表的索引

show logs;：显示BDB存储引擎的日志

show warnings;：显示最后一个执行的语句所产生的错误、警告和通知

show errors;：只显示最后一个执行语句所产生的错误

 desc table_name：显示表信息(字段、分区)

 desc formatted wizad_mdm_raw_hdfs;：显示表详细信息  (字段、分区、路径、格式等)

效果如下：

limit使用:

select * from app_data limit 100;

count:

select count(*) from app_data;

count非常耗费时间，下面有个别人写的小例子。

SELECT type ,
count(*) ,
count(DISTINCT u) ,
count(CASE WHEN plat=1 THEN u ELSE NULL) ,
count(DISTINCT CASE WHEN plat=1 THEN u ELSE NULL) ,
count(CASE WHEN (type=2 OR type=6) THEN u ELSE NULL) ,
count(DISTINCT CASE WHEN (type=2 OR type=6) THEN u ELSE NULL)
FROM t WHERE dt in ("2012-1-12-02", "2012-1-12-03")
GROUP BY type
ORDER BY type ;

  

hive表按partition查询，效率高：

show partitions table_name;：显示表table_name分区

show partitions wizad_mdm_raw_hdfs; ：
day=2014-12-20/adn=3
day=2014-12-21/adn=3
day=2014-12-21/adn=5

descformatted t2 partition (pt = '2014-10-17');：查看分区属性

建分区两种：

1，建表时建分区：

CREATE TABLE tab(

         column1 STRING,

         columnN STRING

) partitioned BY (day STRING);

2，在已存在表上加分区：

alter table wizad_mdm_raw_hdfs add partition (day='2014-12-20',adn='3') location '/user/wizad/data/wizad/raw/2014-12-20/3_1/';
alter table wizad_mdm_raw_hdfs add partition (day='2014-12-20',adn='5') location '/user/wizad/data/wizad/raw/2014-12-20/5_1/';

删除分区：

ALTER TABLE wizad_mdm_raw_hdfs DROP PARTITION (day='2014-12-23',adn='3');
ALTER TABLE wizad_mdm_raw_hdfs DROP PARTITION (day='2014-12-23',adn='5');

修改表

ALTER TABLE old_table_name RENAME TO new_table_name;：重命名

ALTER TABLE tab1 ADD COLUMNS (c1 INT, c2 STRING);：添加字段

创建外部表：

CREATE EXTERNAL TABLE wizad_mdm_dev_lmj_mapping_cookie (
cookie_id STRING,
guid STRING 
) ROW FORMAT DELIMITED 
FIELDS TERMINATED BY ',' 
LINES TERMINATED BY ' '
stored as textfile 
location '/user/wizad/tmp/mapping_cookie/';

格式是：

CREATE EXTERNAL TABLE tab (

column1STRING,

column2STRING,

column3STRING,

column4STRING,

columnNSTRING

) ROW FORMATDELIMITED

FIELDSTERMINATED BY ' '

stored astextfile

location'hdfs://namenode/tmp/lmj/tab/';

hive语句执行环境相关参数设定：

SET mapred.job.queue.name=queue3;
SET hbase.client.scanner.caching=5000;
SET hbase.zookeeper.quorum=datanode06,datanode07,datanode08;
set zookeeper.znode.parent=/hbase;
set hbase.regionserver.lease.period=180000;

将查询结果保存到本地

INSERT OVERWRITE LOCAL DIRECTORY '/home/wizad/lmj/'
ROW FORMAT DELIMITED FIELDS TERMINATED BY ',' 
select cookie_id,rowkey,fixeddim_map
from wizad_mdm_main_from_hbase as a JOIN wizad_mdm_dev_lmj_edition_20141120 as w 
ON (w.guid = a.rowkey);

hive语句性能优化：http://wenku.baidu.com/link?url=eahFKmcvJ08Jj0K8lL6D7Q-6WNwSPlUUzz96MFLDRd0dGwlZEkVvMSwP2RaGtfbvI6dSdBBInTIfBEQXh6iW40COgIFiWkIc1KDHVlNGA_i

这里有一个优化的小例子：http://www.myexception.cn/internet/477451.html