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[Hive - LanguageManual] Alter Table/Partition/Column

2024-11-15 21:12:39   203人阅读

Alter Table/Partition/Column

  • Alter Table
    • Rename Table
    • Alter Table Properties
      • Alter Table Comment
    • Add SerDe Properties
    • Alter Table Storage Properties
    • Additional Alter Table Statements
  • Alter Partition
    • Add Partitions
      • Dynamic Partitions
    • Rename Partition
    • Exchange Partition
    • Recover Partitions (MSCK REPAIR TABLE)
    • Drop Partitions
    • (Un)Archive Partition
  • Alter Either Table or Partition
    • Alter Table/Partition File Format
    • Alter Table/Partition Location
    • Alter Table/Partition Touch
    • Alter Table/Partition Protections
    • Alter Table/Partition Compact
    • Alter Table/Partition Concatenate
  • Alter Column
    • Rules for Column Names
    • Change Column Name/Type/Position/Comment
    • Add/Replace Columns
    • Partial Partition Specification

Alter table statements enable you to change the structure of an existing table. You can add columns/partitions, change SerDe, add table and SerDe properties, or rename the table itself. Similarly, alter table partition statements allow you change the properties of a specific partition in the named table.

Alter Table

Rename Table

ALTER TABLE table_name RENAME TO new_table_name;

This statement lets you change the name of a table to a different name.

As of version 0.6, a rename on a managed table moves its HDFS location as well. (Older Hive versions just renamed the table in the metastore without moving the HDFS location.)

Alter Table Properties

ALTER TABLE table_name SET TBLPROPERTIES table_properties;
 
table_properties:
  : (property_name = property_value, property_name = property_value, ... )

You can use this statement to 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.

Alter Table Comment

To change the comment of a table you have to change the comment property of the TBLPROPERTIES:

ALTER TABLE table_name SET TBLPROPERTIES (‘comment‘ = new_comment);

Add SerDe Properties

ALTER TABLE table_name SET SERDE serde_class_name [WITH SERDEPROPERTIES serde_properties];
 
ALTER TABLE table_name SET SERDEPROPERTIES serde_properties;
 
serde_properties:
  : (property_name = property_value, property_name = property_value, ... )

These statements enable you to change a table‘s SerDe or add user-defined metadata to the table‘s 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 the SerDe documentation and Hive SerDe in the Developer Guide for more information, and see Row Format, Storage Format, and SerDe above for details about setting a table‘s SerDe and SERDEPROPERTIES in a CREATE TABLE statement.

Example, note that both property_name and property_value must be quoted:

ALTER TABLE table_name SET SERDEPROPERTIES (‘field.delim‘ = ‘,‘);

Alter Table Storage Properties

ALTER TABLE table_name CLUSTERED BY (col_name, col_name, ...) [SORTED BY (col_name, ...)]
  INTO num_buckets BUCKETS;

These statements change the table‘s physical storage properties.

NOTE: These commands will only modify Hive‘s metadata, and will NOT reorganize or reformat existing data. Users should make sure the actual data layout conforms with the metadata definition.

Additional Alter Table Statements

See Alter Either Table or Partition below for more DDL statements that alter tables.

Alter Partition

Add Partitions

ALTER TABLE table_name ADD [IF NOT EXISTS] PARTITION partition_spec 
  [LOCATION ‘location1‘] partition_spec [LOCATION ‘location2‘] ...;
 
partition_spec:
  : (partition_column = partition_col_value, partition_column = partition_col_value, ...)

You can use ALTER TABLE ADD PARTITION to add partitions to a table. Partition values should be quoted only if they are strings. The location must be a directory inside of which data files reside. (ADD PARTITION changes the table metadata, but does not load data. If the data does not exist in the partition‘s location, queries will not return any results.)

Note that it is proper syntax to have multiple partition_spec in a single ALTER TABLE, but if you do this in version 0.7, your partitioning scheme will fail. That is, every query specifying a partition will always use only the first partition. Instead, you should use the following form if you want to add many partitions in Hive 0.7:

ALTER TABLE table_name ADD PARTITION (partCol = ‘value1‘) location ‘loc1‘;
ALTER TABLE table_name ADD PARTITION (partCol = ‘value2‘) location ‘loc2‘;
...
ALTER TABLE table_name ADD PARTITION (partCol = ‘valueN‘) location ‘locN‘;

Specifically, the following example (which was the default example before) will FAIL silently and without error, and all queries will go only to dt=‘2008-08-08‘ partition, no matter which partition you specify.

ALTER TABLE page_view ADD PARTITION (dt=‘2008-08-08‘, country=‘us‘) location ‘/path/to/us/part080808‘
                          PARTITION (dt=‘2008-08-09‘, country=‘us‘) location ‘/path/to/us/part080809‘;

In Hive 0.8 and later, you can add multiple partitions in a single ALTER TABLE statement as shown in the previous example.

An error is thrown if the partition_spec for the table already exists. You can use IF NOT EXISTS to skip the error.

Dynamic Partitions

Partitions can be added to a table dynamically, using a Hive INSERT statement (or a Pig STORE statement). See these documents for details and examples:

  • Design Document for Dynamic Partitions
  • Tutorial: Dynamic-Partition Insert
  • Hive DML: Dynamic Partition Inserts
  • HCatalog Dynamic Partitioning
    • Usage with Pig
    • Usage from MapReduce

Rename Partition

Version information

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As of Hive 0.9.

ALTER TABLE table_name PARTITION partition_spec RENAME TO PARTITION partition_spec;

This statement lets you change the value of a partition column.

Exchange Partition

Version information

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As of Hive 0.12 (HIVE-4095).

ALTER TABLE table_name_1 EXCHANGE PARTITION (partition_spec) WITH TABLE table_name_2;

This statement lets you move the data in a partition from a table to another table that has the same schema but does not already have that partition. For details, see Exchange Partition and HIVE-4095.

Recover Partitions (MSCK REPAIR TABLE)

Hive stores a list of partitions for each table in its metastore. If, however, new partitions are directly added to HDFS (say by using hadoop fs -put command), the metastore (and hence Hive) will not be aware of these partitions unless the user runs ALTER TABLE table_name ADD PARTITION commands on each of the newly added partitions.

However, users can run

MSCK REPAIR TABLE table_name;

which will add metadata about partitions to the Hive metastore for partitions for which such metadata doesn‘t already exist. In other words, it will add any partitions that exist on HDFS but not in metastore to the metastore. See HIVE-874 for more details.

The equivalent command on Amazon Elastic MapReduce (EMR)‘s version of Hive is

ALTER TABLE table_name RECOVER PARTITIONS;

Drop Partitions

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

You can use ALTER TABLE DROP PARTITION to drop a partition for a table. This removes the data and metadata for this partition.

For tables that are protected by NO_DROP CASCADE, you can use the predicate IGNORE PROTECTION to drop a specified partition or set of partitions (for example, when splitting a table between two Hadoop clusters).

ALTER TABLE table_name DROP [IF EXISTS] PARTITION partition_spec IGNORE PROTECTION;

The above command will drop that partition regardless of protection stats.

In Hive 0.7.0 or later, DROP returns an error if the partition doesn‘t exist, unless IF EXISTS is specified or the configuration variable hive.exec.drop.ignorenonexistent is set to true.

ALTER TABLE page_view DROP PARTITION (dt=‘2008-08-08‘, country=‘us‘);

(Un)Archive Partition

ALTER TABLE table_name ARCHIVE PARTITION partition_spec;
ALTER TABLE table_name UNARCHIVE PARTITION partition_spec;

Archiving is a feature to moves a partition‘s files into a Hadoop Archive (HAR). Note that only the file count will be reduced; HAR does not provide any compression. See LanguageManual Archiving for more information

Alter Either Table or Partition

Alter Table/Partition File Format

ALTER TABLE table_name [PARTITION partition_spec] SET FILEFORMAT file_format;

This statement changes the table‘s (or partition‘s) file format. For available file_format options, see the section above on CREATE TABLE.

Alter Table/Partition Location

ALTER TABLE table_name [PARTITION partition_spec] SET LOCATION "new location";

Alter Table/Partition Touch

ALTER TABLE table_name TOUCH [PARTITION partition_spec];

TOUCH reads the metadata, and writes it back. This has the effect of causing the pre/post execute hooks to fire. An example use case is if you have a hook that logs all the tables/partitions that were modified, along with an external script that alters the files on HDFS directly. Since the script modifies files outside of hive, the modification wouldn‘t be logged by the hook. The external script could call TOUCH to fire the hook and mark the said table or partition as modified.

Also, it may be useful later if we incorporate reliable last modified times. Then touch would update that time as well.

Note that TOUCH doesn‘t create a table or partition if it doesn‘t already exist. (See Create Table.)

Alter Table/Partition Protections

Version information

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As of Hive 0.7.0 (HIVE-1413). The CASCADE clause for NO_DROP was added in HIVE 0.8.0 (HIVE-2605).

ALTER TABLE table_name [PARTITION partition_spec] ENABLE|DISABLE NO_DROP [CASCADE];
 
ALTER TABLE table_name [PARTITION partition_spec] ENABLE|DISABLE OFFLINE;

Protection on data can be set at either the table or partition level. Enabling NO_DROP prevents a table from being dropped. Enabling OFFLINE prevents the data in a table or partition from being queried, but the metadata can still be accessed.

If any partition in a table has NO_DROP enabled, the table cannot be dropped either. Conversely, if a table has NO_DROP enabled then partitions may be dropped, but with NO_DROP CASCADE then partitions cannot be dropped either.

Alter Table/Partition Compact

Version information

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In Hive release 0.13.0 and later when transactions are being used, the ALTER TABLE statement can request compaction of a table or partition.

ALTER TABLE table_name [PARTITION (partition_key = ‘partition_value‘ [, ...])]
  COMPACT ‘compaction_type‘;

In general you do not need to request compactions when Hive transactions are being used, because the system will detect the need for them and initiate the compaction. However, if compaction is turned off for a table or you want to compact the table at a time the system would not choose to, ALTER TABLE can initiate the compaction. The statement will enqueue a request for compaction and return. To watch the progress of the compaction, use SHOW COMPACTIONS.

The compaction_type can be MAJOR or MINOR. See the Basic Design section in Hive Transactions for more information.

Alter Table/Partition Concatenate

Version information

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In Hive release 0.8.0 RCFile added support for fast block level merging of small RCFiles using concatenate command. In Hive release 0.14.0 ORC files added support fast stripe level merging of small ORC files using concatenate command.

ALTER TABLE table_name [PARTITION (partition_key = ‘partition_value‘ [, ...])] CONCATENATE;

If the table or partition contains many small RCFiles or ORC files, then the above command will merge them into larger files. In case of RCFile the merge happens at block level whereas for ORC files the merge happens at stripe level thereby avoiding the overhead of decompressing and decoding the data.

Alter Column

Rules for Column Names

Column names are case insensitive.

Version information

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In Hive release 0.12.0 and earlier, column names can only contain alphanumeric and underscore characters.

In Hive release 0.13.0 and later, by default column names can be specified within backticks (`) and contain any Unicode character (HIVE-6013). Within a string delimited by backticks, all characters are treated literally except that double backticks (``) represent one backtick character. The pre-0.13.0 behavior can be used by setting hive.support.quoted.identifiers to none, in which case backticked names are interpreted as regular expressions. See Supporting Quoted Identifiers in Column Names for details.

Change Column Name/Type/Position/Comment

ALTER TABLE table_name [PARTITION partition_spec] CHANGE [COLUMN] col_old_name col_new_name column_type
  [COMMENT col_comment] [FIRST|AFTER column_name] [CASCADE|RESTRICT];

This command will allow users to change a column‘s name, data type, comment, or position, or an arbitrary combination of them. The PARTITION clause is available in Hive 0.14.0 and later; seeUpgrading Pre-Hive 0.13.0 Decimal Columns for usage. A patch for Hive 0.13 is also available (see HIVE-7971).

The CASCADE|RESTRICT clause is available in Hive 0.15.0. ALTER TABLE CHANGE COLUMN with CASCADE command changes the columns of a table‘s metadata, and cascades the same change to all the partition metadata. RESTRICT is the default, limiting column change only to table metadata.

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ALTER TABLE CHANGE COLUMN CASCADE clause will override the table partition‘s column metadata regardless of the table or partition‘s protection mode. Use with discretion.

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The column change command will only modify Hive‘s metadata, and will not modify data. Users should make sure the actual data layout of the table/partition conforms with the metadata definition.

Example:

CREATE TABLE test_change (a int, b int, c int);
 
// First change column a‘s name to a1.
ALTER TABLE test_change CHANGE a a1 INT;
 
// Next change column a1‘s name to a2, its data type to string, and put it after column b.
ALTER TABLE test_change CHANGE a1 a2 STRING AFTER b;
// The new table‘s structure is:  b int, a2 string, c int.
 
// Then change column c‘s name to c1, and put it as the first column.
ALTER TABLE test_change CHANGE c c1 INT FIRST;
// The new table‘s structure is:  c1 int, b int, a2 string.

 

Add/Replace Columns

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

ADD COLUMNS lets you add new columns to the end of the existing columns but before the partition columns. This is supported for Avro backed tables as well, for Hive 0.14 and later. The PARTITION clause is available in Hive 0.14.0 and later; REPLACE COLUMNS removes all existing columns and adds the new set of columns. This can be done only for tables with native SerDe (DynamicSerDe, MetadataTypedColumnsetSerDe, LazySimpleSerDe and ColumnarSerDe). Refer to Hive SerDe for more information. REPLACE COLUMNS can also be used to drop columns. For example:

"ALTER TABLE test_change REPLACE COLUMNS (a int, b int);" will remove column ‘c‘ from test_change‘s schema.

The PARTITION clause is available in Hive 0.14.0 and later; see Upgrading Pre-Hive 0.13.0 Decimal Columns for usage.

The CASCADE|RESTRICT clause is available in Hive 0.15.0. ALTER TABLE ADD|REPLACE COLUMNS with CASCADE command changes the columns of a table‘s metadata, and cascades the same change to all the partition metadata. RESTRICT is the default, limiting column changes only to table metadata.

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 ALTER TABLE ADD|REPLACE COLUMNS CASCADE clause will override the table partition‘s column metadata regardless of the table or partition‘s protection mode. Use with discretion.
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The column change command will only modify Hive‘s metadata, and will not modify data. Users should make sure the actual data layout of the table/partition conforms with the metadata definition.

Partial Partition Specification

As of Hive 0.14 (HIVE-8411), users are able to provide a partial partition spec for certain above alter column statements, similar to dynamic partitioning. So rather than having to issue an alter column statement for each partition that needs to be changed:

ALTER TABLE foo PARTITION (ds=‘2008-04-08‘, hr=11) CHANGE COLUMN dec_column_name dec_column_name DECIMAL(38,18);
ALTER TABLE foo PARTITION (ds=‘2008-04-08‘, hr=12) CHANGE COLUMN dec_column_name dec_column_name DECIMAL(38,18);
...

... you can change many existing partitions at once using a single ALTER statement with a partial partition specification:

// hive.exec.dynamic.partition needs to be set to true to enable dynamic partitioning with ALTER PARTITION
SET hive.exec.dynamic.partition = true;
  
// This will alter all existing partitions in the table with ds=‘2008-04-08‘ -- be sure you know what you are doing!
ALTER TABLE foo PARTITION (ds=‘2008-04-08‘, hr) CHANGE COLUMN dec_column_name dec_column_name DECIMAL(38,18);
 
// This will alter all existing partitions in the table -- be sure you know what you are doing!
ALTER TABLE foo PARTITION (ds, hr) CHANGE COLUMN dec_column_name dec_column_name DECIMAL(38,18);

 

Similar to dynamic partitioning, hive.exec.dynamic.partition must be set to true to enable use of partial partition specs during ALTER PARTITION. This is supported for the following operations:

  • Change column
  • Add column
  • Replace column
  • File Format
  • Serde Properties

 

[Hive - LanguageManual] Alter Table/Partition/Column


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