hadoop-common-commits mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Update of "Hive/LanguageManual/DDL" by HeYongqiang
Date Wed, 23 Dec 2009 22:11:53 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Hadoop Wiki" for change notification.

The "Hive/LanguageManual/DDL" page has been changed by HeYongqiang.
http://wiki.apache.org/hadoop/Hive/LanguageManual/DDL?action=diff&rev1=23&rev2=24

--------------------------------------------------

  == Create/Drop Table and Partition Statements ==
  === Create Table ===
  {{{
- CREATE [EXTERNAL] TABLE [IF NOT EXISTS] table_name 
+ CREATE [EXTERNAL] TABLE [IF NOT EXISTS] table_name
    [(col_name data_type [COMMENT col_comment], ...)]
    [table_comment]
    [PARTITIONED BY (col_name data_type [col_comment], col_name data_type [COMMENT col_comment],
...)]
@@ -30, +30 @@

    | STRING
  
  array_type
-   : ARRAY < primitive_type > 
+   : ARRAY < primitive_type >
  
  map_type
    : MAP < primitive_type, primitive_type >
  
  row_format
-   : DELIMITED [FIELDS TERMINATED BY char] [COLLECTION ITEMS TERMINATED BY char] 
+   : DELIMITED [FIELDS TERMINATED BY char] [COLLECTION ITEMS TERMINATED BY char]
          [MAP KEYS TERMINATED BY char]
    | SERDE serde_name [WITH SERDEPROPERTIES property_name=property_value, property_name=property_value,
...]
  
  file_format:
    : SEQUENCEFILE
    | TEXTFILE
- 
  }}}
- 
  CREATE TABLE creates a table with given name. An error is thrown if a table with the same
name exists. You can use IF NOT EXISTS to skip the error.
  
  EXTERNAL keyword lets you create a table and provide a LOCATION so that Hive does not use
default location for this table. This comes in handy if you already have data generated. When
dropping an EXTERNAL table, data in the table is NOT deleted from the file system.
  
  You can create tables with custom SerDe or using native SerDe. A native SerDe is used if
ROW FORMAT is not specified or ROW FORMAT DELIMITED is specified. You can use DELIMITED clause
to read delimited files. Use SERDE clause to create a table with custom SerDe. Refer to SerDe
section of User Guide for more information on SerDe.
-  
+ 
  You must specify list of columns for tables with native SerDe. Refer to Types part of the
User Guide for the allowable column types. List of columns for tables with custom SerDe may
be specified but Hive will query the SerDe to determine the list of columns for this table.
  
  Use STORED AS TEXTFILE if the data needs to be stored as plain text files. Use STORED AS
SEQUENCEFILE if the data needs to be compressed. Please read more about CompressedStorage
if you are planning to keep data compressed in your Hive tables.
@@ -62, +60 @@

  
  Tables can also be created and populated by the results of a query in one CTAS (create-table-as-select)
statement. The table created by CTAS is atomic, meaning that the table is not seen by other
users until all the query results are populated. So other users will either see the table
with the complete results of the query or will not see the table at all.
  
- There are two parts in CTAS, the SELECT part can be any [[Hive/LanguageManual/Select|SELECT
statement]] supported by HiveQL. The CREATE part of the CTAS takes the resulting schema from
the SELECT part and create the target table with other table properties such as the SerDe
and storage format. The only restrictions in CTAS is that the target table cannot be a partitioned
table nor an external table. 
+ There are two parts in CTAS, the SELECT part can be any [[Hive/LanguageManual/Select|SELECT
statement]] supported by HiveQL. The CREATE part of the CTAS takes the resulting schema from
the SELECT part and create the target table with other table properties such as the SerDe
and storage format. The only restrictions in CTAS is that the target table cannot be a partitioned
table nor an external table.
  
  Examples:
  
- An example statement that would create a table would be like: 
+ An example statement that would create a table would be like:
  
  {{{
- CREATE TABLE page_view(viewTime INT, userid BIGINT, 
+ CREATE TABLE page_view(viewTime INT, userid BIGINT,
-      page_url STRING, referrer_url STRING, 
+      page_url STRING, referrer_url STRING,
-      ip STRING COMMENT 'IP Address of the User') 
+      ip STRING COMMENT 'IP Address of the User')
-  COMMENT 'This is the page view table' 
+  COMMENT 'This is the page view table'
-  PARTITIONED BY(dt STRING, country STRING) 
+  PARTITIONED BY(dt STRING, country STRING)
   STORED AS SEQUENCEFILE;
  }}}
- 
- The statement above creates page_view table with viewTime, userid, page_url, referrer_url,
up columns with a comment. The table is also partitioned and data is stored in sequence files.
The data in the files assumed to be field delimited by ctrl-A and row delimited by newline.

+ The statement above creates page_view table with viewTime, userid, page_url, referrer_url,
up columns with a comment. The table is also partitioned and data is stored in sequence files.
The data in the files assumed to be field delimited by ctrl-A and row delimited by newline.
  
  {{{
- CREATE TABLE page_view(viewTime INT, userid BIGINT, 
+ CREATE TABLE page_view(viewTime INT, userid BIGINT,
-      page_url STRING, referrer_url STRING, 
+      page_url STRING, referrer_url STRING,
-      ip STRING COMMENT 'IP Address of the User') 
+      ip STRING COMMENT 'IP Address of the User')
-  COMMENT 'This is the page view table' 
+  COMMENT 'This is the page view table'
-  PARTITIONED BY(dt STRING, country STRING) 
+  PARTITIONED BY(dt STRING, country STRING)
-  ROW FORMAT DELIMITED 
+  ROW FORMAT DELIMITED
-    FIELDS TERMINATED BY '\001' 
+    FIELDS TERMINATED BY '\001'
  STORED AS SEQUENCEFILE;
  }}}
- 
  The above statement lets you to create same table as previous table.
  
  {{{
- CREATE TABLE page_view(viewTime INT, userid BIGINT, 
+ CREATE TABLE page_view(viewTime INT, userid BIGINT,
-      page_url STRING, referrer_url STRING, 
+      page_url STRING, referrer_url STRING,
-      ip STRING COMMENT 'IP Address of the User') 
+      ip STRING COMMENT 'IP Address of the User')
-  COMMENT 'This is the page view table' 
+  COMMENT 'This is the page view table'
-  PARTITIONED BY(dt STRING, country STRING) 
+  PARTITIONED BY(dt STRING, country STRING)
-  CLUSTERED BY(userid) SORTED BY(viewTime) INTO 32 BUCKETS 
+  CLUSTERED BY(userid) SORTED BY(viewTime) INTO 32 BUCKETS
-  ROW FORMAT DELIMITED 
+  ROW FORMAT DELIMITED
-    FIELDS TERMINATED BY '\001' 
+    FIELDS TERMINATED BY '\001'
-    COLLECTION ITEMS TERMINATED BY '\002' 
+    COLLECTION ITEMS TERMINATED BY '\002'
-    MAP KEYS TERMINATED BY '\003' 
+    MAP KEYS TERMINATED BY '\003'
   STORED AS SEQUENCEFILE;
  }}}
- 
- In the example above, the page_view table is bucketed(clustered by) userid and within each
bucket the data is sorted in the increasing order of viewTime. Such an organization allows
the user to do efficient sampling on the clustered column - in this case userid. The sorting
property allows internal operators to take advantage of the better-known data structure while
evaluating queries, also increasing efficiency. MAP KEYS and COLLECTION ITEMS keywords can
be used if any of the columns are lists or maps. 
+ In the example above, the page_view table is bucketed(clustered by) userid and within each
bucket the data is sorted in the increasing order of viewTime. Such an organization allows
the user to do efficient sampling on the clustered column - in this case userid. The sorting
property allows internal operators to take advantage of the better-known data structure while
evaluating queries, also increasing efficiency. MAP KEYS and COLLECTION ITEMS keywords can
be used if any of the columns are lists or maps.
  
- In all the examples until now the data is stored in <hive.metastore.warehouse.dir>/page_view.
Specify value of the key hive.metastore.warehouse.dir in Hive config file hive-site.xml. 
+ In all the examples until now the data is stored in <hive.metastore.warehouse.dir>/page_view.
Specify value of the key hive.metastore.warehouse.dir in Hive config file hive-site.xml.
  
  {{{
- CREATE EXTERNAL TABLE page_view(viewTime INT, userid BIGINT, 
+ CREATE EXTERNAL TABLE page_view(viewTime INT, userid BIGINT,
-      page_url STRING, referrer_url STRING, 
+      page_url STRING, referrer_url STRING,
-      ip STRING COMMENT 'IP Address of the User', 
+      ip STRING COMMENT 'IP Address of the User',
-      country STRING COMMENT 'country of origination') 
+      country STRING COMMENT 'country of origination')
-  COMMENT 'This is the staging page view table' 
+  COMMENT 'This is the staging page view table'
   ROW FORMAT DELIMITED FIELDS TERMINATED BY '\054'
-  STORED AS TEXTFILE 
+  STORED AS TEXTFILE
   LOCATION '<hdfs_location>';
  }}}
- 
  You can use above statement to create page_view table which points to data location any
hdfs location. But you have to make sure that the data is delimited as specified in the query
above.
  
- 
  {{{
  CREATE TABLE new_key_value_store
-    ROW FORMAT SERDE "org.apache.hadoop.hive.serde2.columnar.ColumnarSerDe" 
+    ROW FORMAT SERDE "org.apache.hadoop.hive.serde2.columnar.ColumnarSerDe"
-    STORED AS RCFile AS 
+    STORED AS RCFile AS
- SELECT (key % 1024) new_key, concat(key, value) key_value_pair 
+ SELECT (key % 1024) new_key, concat(key, value) key_value_pair
  FROM key_value_store
  SORT BY new_key, key_value_pair;
  }}}
- 
- The above CTAS statement creates the target table new_key_value_store with the schema, (new_key
DOUBLE, key_value_pair STRING), derived from the results of the SELECT statement. If the SELECT
statement does not specify column aliases, the column names will be automatically assigned
to _col0, _col1, and _col2 etc. In addition, the new target table is created using a specific
SerDe and a storage format independent of the source tables in the SELECT statement. 
+ The above CTAS statement creates the target table new_key_value_store with the schema, (new_key
DOUBLE, key_value_pair STRING), derived from the results of the SELECT statement. If the SELECT
statement does not specify column aliases, the column names will be automatically assigned
to _col0, _col1, and _col2 etc. In addition, the new target table is created using a specific
SerDe and a storage format independent of the source tables in the SELECT statement.
  
  ==== Inserting Data Into Bucketed Tables ====
  The CLUSTER BY and SORTED BY creation commands do not effect how data is inserted into a
table -- only how it is read.  This means that users must actively insert data correctly by
specifying the number of reducers to be equal to the number of buckets, and using CLUSTER
BY and SORT BY commands in their query.
@@ -144, +136 @@

  {{{
  DROP TABLE table_name
  }}}
- 
  DROP TABLE removes metadata and data for this table. The data is actually moved to the .Trash/Current
directory if Trash is configured. The metadata is completely lost.
  
  When dropping an EXTERNAL table, data in the table will NOT deleted from the file system.
@@ -156, +147 @@

  partition_spec:
    : PARTITION (partition_col = partition_col_value, partition_col = partiton_col_value,
...)
  }}}
- 
  You can use ALTER TABLE DROP PARTITION to drop a partition for a table. This removes the
data and metadata for this partition. Partition value should be quoted only if it is a string.
  
  {{{
  alter table page_view drop partition(dt='2008-08-08', country='us')
- }}} 
+ }}}
+ 
  
  == Alter Table Statements ==
  Alter table statements enable you to change the structure of an existing table. You can
add columns, change serde, add table and serde properties, or rename the table itself.
@@ -170, +161 @@

  {{{
  ALTER TABLE table_name RENAME TO new_table_name
  }}}
- 
- This statement lets you change the name of a table to a different name. '''The location
of the data and the names of partitions do not change!''' In other words, the old table name
is not "freed," and writing to it will alter the "renamed" table's data! 
+ This statement lets you change the name of a table to a different name. '''The location
of the data and the names of partitions do not change!''' In other words, the old table name
is not "freed," and writing to it will alter the "renamed" table's data!
+ 
+ === Change Column Name/Type/Position/Comment ===
+ {{{
+ ALTER TABLE table_name CHANGE [COLUMN] col_old_name col_new_name column_type [COMMENT col_comment]
[FIRST|AFTER column_name]
+ }}}
+ 
+ This command will allow users to change a column's name, data type, comment, or position,
or a arbitrary combination of them.
+ 
+ Example:
+ create table test_change (a int, b int, c int);
+ 
+ "alter table change a a1 int;" will change column a's name to a1.
+ 
+ "alter table change a a1 string after b;" will change column a's name to a1, a's data type
to string, and put it after column b. The new table's structure is: b int, a1 string, c int.
+ 
+ "alter table change b b1 int first;" will change column b's name to b1, and put it as the
first column. The new table's structure is: b1 int, a string, c int.
+ 
+ NOTE: The column change command will only modify Hive's metadata, and will NOT touch data.
Users should make sure the actual data layout conforms with the metadata definition.
  
  === Add/Replace Columns ===
  {{{
  ALTER TABLE table_name ADD|REPLACE COLUMNS (col_name data_type [COMMENT col_comment], ...)
  }}}
- 
  ADD COLUMNS lets you add new columns to the end of the existing columns but before the partition
columns.
  
  REPLACE COLUMNS removes all existing columns and adds the new set of columns. This can be
done only for native tables. Native tables are those tables that are created with DynamicSerDe
or MetadataTypedColumnsetSerDe serdes. Refer to SerDe section of User Guide for more information.
@@ -189, +196 @@

  table_properties:
    : (property_key = property_value, property_key = property_value, ... )
  }}}
- 
  You can use this statement add your own metadata to the tables. Currently last_modified_user,
last_modified_time properties are automatically added and managed by Hive. Users can add their
own properties to this list. You can do DESCRIBE EXTENDED TABLE to get this information.
  
  === Add Serde Properties ===
@@ -200, +206 @@

  serde_properties:
    : (property_key = property_value, property_key = property_value, ... )
  }}}
- 
  This statement enables you to add user defined metadata to table SerDe object. The serde
properties are passed to the table's SerDe when it is being initialized by Hive to serialize
and deserialize data. So users can store any information required for their custom serde here.
Refer to SerDe section of Users Guide for more information.
  
  == Show/Describe Statements ==
@@ -210, +215 @@

  {{{
  SHOW TABLES identifier_with_wildcards
  }}}
- 
  SHOW TABLES lists all the tables matching the given regular expression. Regular expression
can contain only '*' for any character[s] or '|' for a choice. Examples are 'page_view', 'page_v*',
'*view|page*', all which will match 'page_view' table. Matching tables are listed in alphabetical
order. It is not an error if there are no matching tables found in metastore.
  
  === Show Partitions ===
  {{{
  SHOW PARTITIONS table_name
  }}}
- 
  SHOW PARTITIONS lists all the existing partitions for a given table. Partitions are listed
in alphabetical order.
  
  === Describe Table/Column ===
@@ -225, +228 @@

  DESCRIBE [EXTENDED] table_name[DOT col_name]
  DESCRIBE [EXTENDED] table_name[DOT col_name ( [DOT field_name] | [DOT '$elem$'] | [DOT '$key$']
| [DOT '$value$'] )* ]
  }}}
- 
  DESCRIBE TABLE shows the list of columns including partition column for the given table.
If EXTENDED keyword is specified then it will show all the metadata for the table in Thrift
serialized form. This is generally only useful for debugging and not for general use.
  
  If a table has complex column then you can examine the attributes of this column by specifying
table_name.complex_col_name (and '$elem$' for array element, '$key$' for map key, and '$value$'
for map value). You can specify this recursively to explore the complex column type.
@@ -234, +236 @@

  {{{
  DESCRIBE [EXTENDED] table_name partition_spec
  }}}
- 
  This statement lists metadata for a given partition. The output is similar to that of DESCRIBE
TABLE. Presently, the column information is not used while preparing plans.
  
  === Create Function ===
  {{{
- CREATE TEMPORARY FUNCTION function_name AS class_name 
+ CREATE TEMPORARY FUNCTION function_name AS class_name
  }}}
- 
  This statement lets you create a function that is implemented by the class_name. You can
use this function in Hive queries as long as the session lasts. You can use any class that
is in the class path of Hive. You can add jars to class path by executing 'ADD FILES' statements.
Please refer to CLI section in User Guide for more information on how to add/delete files
from Hive classpath. Using this you can define User Defined Functions.
  

Mime
View raw message