hive修改表模式

转载：http://blog.csdn.net/yfkiss/article/details/7859477

学习网址：http://www.360doc.com/content/12/0111/11/7362_178698714.shtml

hive用户可以通过alter语句更改table属性

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, ...)

删除partitions：

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

示例：

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可以同时增加或者删除多个partition
2. 使用location关键字时，增加的partition以类似extend table数据的形式存在外部。

Alter Column
修改column属性（列名，列字段类型，列注释）：

ALTER TABLE table_name
      CHANGE [COLUMN] col_old_name col_new_name
      column_type [COMMENT col_comment] [FIRST|AFTER column_name]

增加/替换column（可以使用replace来删除不需要的字段）：

ALTER TABLE table_name
      ADD|REPLACE COLUMNS (col_name data_type [COMMENT col_comment], ...)

示例：

hive> alter table alter_test add columns(test_columen INT);
OK
Time taken: 2.096 seconds
hive> desc alter_test;
OK
id      int
name    string
test_columen    int
dt      string
Time taken: 0.345 seconds
hive> select * from alter_test;
OK
3       cds     NULL    2012-08-11
4       mac     NULL    2012-08-11
1       zxm     NULL    2012-08-12
2       ljz     NULL    2012-08-12
1       zxm     NULL    2012-08-13
2       ljz     NULL    2012-08-13
Time taken: 8.467 seconds
hive> alter table alter_test replace columns (id int, name string);
OK
Time taken: 0.217 seconds
hive> desc alter_test;
OK
id      int
name    string
dt      string
Time taken: 0.181 seconds
hive> select * from alter_test;
OK
3       cds     2012-08-11
4       mac     2012-08-11
1       zxm     2012-08-12
2       ljz     2012-08-12
1       zxm     2012-08-13
2       ljz     2012-08-13
Time taken: 0.364 seconds
hive> alter table alter_test change id myid INT;
OK
Time taken: 0.259 seconds
hive> desc alter_test;
OK
myid    int
name    string
dt      string
Time taken: 0.053 seconds

注意：column alter仅仅修改table的元数据，而不会修改数据。