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[Hive - LanguageManual] Describe

2024-11-15 20:37:02   202人阅读

Describe

  • Describe Database
  • Describe Table/View/Column
    • Display Column Statistics
  • Describe Partition

Describe Database

Version information

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As of Hive 0.7.

DESCRIBE DATABASE [EXTENDED] db_name;
DESCRIBE SCHEMA [EXTENDED] db_name;     -- (Note: Hive 0.15.0 and later)

DESCRIBE DATABASE shows the name of the database, its comment (if one has been set), and its root location on the filesystem. The uses of SCHEMA and DATABASE are interchangeable – they mean the same thing. DESCRIBE SCHEMA is added in Hive 0.15 (HIVE-8803).

EXTENDED also shows the database properties.

Describe Table/View/Column

DESCRIBE [EXTENDED|FORMATTED]
  [db_name.]table_name[.col_name ( [.field_name] | [.‘$elem$‘] | [.‘$key$‘] | [.‘$value$‘] )* ];

DESCRIBE shows the list of columns including partition columns for the given table. If the 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 the FORMATTED keyword is specified, then it will show the metadata in a tabular format.

Note: DESCRIBE EXTENDED shows the number of rows only if statistics were gathered when the data was loaded (see Newly Created Tables), and if the Hive CLI is used instead of a Thrift client or Beeline. HIVE-6285 will address this issue. Although ANALYZE TABLE gathers statistics after the data has been loaded (see Existing Tables), it does not currently provide information about the number of rows.

If a table has a 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.

For a view, DESCRIBE EXTENDED or FORMATTED can be used to retrieve the view‘s definition. Two relevant attributes are provided: both the original view definition as specified by the user, and an expanded definition used internally by Hive.

Version information

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In Hive 0.10.0 and earlier, no distinction is made between partition columns and non-partition columns while displaying columns for DESCRIBE TABLE. From Hive 0.12.0 onwards, they are displayed separately.

In Hive 0.13.0 and later, the configuration parameter hive.display.partition.cols.separately lets you use the old behavior, if desired (HIVE-6689). For an example, see the test case in the patch for HIVE-6689.

Bug fixed in Hive 0.10.0

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Database qualifiers for table names were introduced in Hive 0.7.0, but they were broken for DESCRIBE until a bug fix in Hive 0.10.0 (HIVE-1977).

Display Column Statistics

Version information

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As of Hive 0.14.0; see HIVE-7050 and HIVE-7051. (The FOR COLUMNS option of ANALYZE TABLE is available as of Hive 0.10.0.)

ANALYZE TABLE table_name COMPUTE STATISTICS FOR COLUMNS will compute column statistics for all columns in the specified table (and for all partitions if the table is partitioned). To view the gathered column statistics, the following statements can be used:

DESCRIBE FORMATTED [db_name.]table_name.column_name;                              -- (Note: Hive 0.14.0 and later)
DESCRIBE FORMATTED [db_name.]table_name.column_name PARTITION (partition_spec);   -- (Note: Hive 0.14.0 and later)

See Statistics in Hive: Existing Tables for more information about the ANALYZE TABLE command.

Describe Partition

DESCRIBE [EXTENDED|FORMATTED] [db_name.]table_name PARTITION partition_spec;

This statement lists metadata for a given partition. The output is similar to that of DESCRIBE table_name. Presently, the column information associated with a particular partition is not used while preparing plans.

Example:

DESCRIBE page_view PARTITION (ds=‘2008-08-08‘);

[Hive - LanguageManual] Describe


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