Hive修改表模式

Hive使用者可以通過alter語句更改table屬性

Alter Partitions
增加partitions：

ALTER TABLE table_name
      ADD [IF NOT EXISTS]
      PARTITION partition_spec [LOCATION 'location1']
                partition_spec [LOCATION 'location2'] ...
partition_spec:
      (partition_col = partition_col_value, partition_col = partiton_col_value, ...)

刪除partitions：

ALTER TABLE table_name DROP [IF EXISTS] partition_spec, partition_spec,...

樣本：

hive> create table alter_test(id INT, name STRING) 
    > partitioned by(dt STRING)                   
    > row format delimited fields terminated by ',';
OK
Time taken: 0.259 seconds
hive> create table alter_tmp(id INT, name STRING，dt STRING)
    > row format delimited fields terminated by ',';
OK
Time taken: 2.078 seconds
hive> load data local inpath '/home/work/data/alter_test.txt' into table alter_tmp;
Copying data from file:/home/work/data/alter_test.txt
Copying file: file:/home/work/data/alter_test.txt
Loading data to table default.alter_tmp
OK
Time taken: 2.71 seconds
hive> set hive.exec.dynamic.partition.mode=nonstrict;
hive> set hive.exec.dynamic.partition=true;
hive> insert overwrite table alter_test partition(dt)
    > select id,name,dt                             
    > from alter_tmp; 
OK
Time taken: 25.988 seconds
$ cat alter_test2.txt
1,zxm,2012-08-13
2,ljz,2012-08-13
$ Hadoop fs -put alter_test2.txt /data/
hive> alter table alter_test add partition(dt='2012-08-13') location '/data';               
OK
Time taken: 8.717 seconds
$ hadoop fs -ls /user/hive/warehouse/alter_test/
Found 3 items
drwxr-xr-x   - work supergroup          0 2012-08-12 20:50 /user/hive/warehouse/alter_test/dt=2012-08-10
drwxr-xr-x   - work supergroup          0 2012-08-12 20:50 /user/hive/warehouse/alter_test/dt=2012-08-11
drwxr-xr-x   - work supergroup          0 2012-08-12 20:50 /user/hive/warehouse/alter_test/dt=2012-08-12
hive> select * from alter_test where dt='2012-08-13'; 
OK
1      zxm    2012-08-13
2      ljz    2012-08-13
Time taken: 6.064 seconds
$ hadoop fs -rmr  /data
hive> select * from alter_test where dt='2012-08-13'; 
OK
Time taken: 1.903 seconds
hive> show partitions alter_test;
OK
dt=2012-08-10
dt=2012-08-11
dt=2012-08-12
dt=2012-08-13
Time taken: 0.546 seconds
> alter table alter_test add partition(dt='2012-08-14') partition(dt='2012-08-15');      
OK
Time taken: 0.57 seconds
hive> alter table alter_test drop partition(dt='2012-08-10');                           
Dropping the partition dt=2012-08-10
OK
Time taken: 4.509 seconds
$ hadoop fs -ls /user/hive/warehouse/alter_test/ 
Found 4 items
drwxr-xr-x   - work supergroup          0 2012-08-12 20:50 /user/hive/warehouse/alter_test/dt=2012-08-11
drwxr-xr-x   - work supergroup          0 2012-08-12 20:50 /user/hive/warehouse/alter_test/dt=2012-08-12
drwxr-xr-x   - work supergroup          0 2012-08-13 02:15 /user/hive/warehouse/alter_test/dt=2012-08-14
drwxr-xr-x   - work supergroup          0 2012-08-13 02:15 /user/hive/warehouse/alter_test/dt=2012-08-15

注意：
1. hive可以同時增加或者刪除多個partition
2. 使用location關鍵字時，增加的partition以類似extend table資料的形式存在外部。

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