hive修改表模式
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：
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：
注意：column alter仅仅修改table的元数据，而不会修改hdfs上的数据文件
其它：
hive alter语句还支持：
1.Alter Table Properties
2.Alter SerDe Properties
3.Alter Table/Partition File Format
4.Alter Table Storage Properties
5.Alter Table/Partition Location
6.Alter Table Touch
7.Alter Table (Un)Archive
8.Alter Table/Partition Protections
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hdfs上的数据文件
hive> select * from product;
OK
id name
1 apple
2 samsung
3 moto
1 apple
执行删除列：
hive> alter table product replace columns(name string);
OK
Time taken: 0.215 seconds
hive> select * from product;
OK
name
1
2
3
1
2
发现其实这并不是我们想要的，后面的列值往前移动了
而数据文件也没有什么变化
hive> dfs -cat /user/hive/warehouse/psi.db/product/000000_0;
1 apple
2 samsung
3 moto
1 apple
2 samsung其它：
hive alter语句还支持：
1.Alter Table Properties
2.Alter SerDe Properties
3.Alter Table/Partition File Format
4.Alter Table Storage Properties
5.Alter Table/Partition Location
6.Alter Table Touch
7.Alter Table (Un)Archive
8.Alter Table/Partition Protections
9.Alter Table Rename Partition
参考：
http://blog.csdn.net/yfkiss/article/details/7859477