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Cherry-picks: not for 2.x. Change-Id: I094e00c2a4e8b19226e06afd8cf67968265edc4d Reviewed-on: http://gerrit.cloudera.org:8080/9996 Reviewed-by: Alex Behm <alex.behm@cloudera.com> Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
808 lines
42 KiB
XML
808 lines
42 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!--
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Licensed to the Apache Software Foundation (ASF) under one
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or more contributor license agreements. See the NOTICE file
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distributed with this work for additional information
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regarding copyright ownership. The ASF licenses this file
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to you under the Apache License, Version 2.0 (the
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"License"); you may not use this file except in compliance
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with the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing,
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software distributed under the License is distributed on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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KIND, either express or implied. See the License for the
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specific language governing permissions and limitations
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under the License.
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-->
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
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<concept id="describe">
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<title id="desc">DESCRIBE Statement</title>
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<titlealts audience="PDF"><navtitle>DESCRIBE</navtitle></titlealts>
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<prolog>
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<metadata>
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<data name="Category" value="Impala"/>
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<data name="Category" value="Impala Data Types"/>
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<data name="Category" value="SQL"/>
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<data name="Category" value="Developers"/>
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<data name="Category" value="Data Analysts"/>
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<data name="Category" value="Tables"/>
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<data name="Category" value="Reports"/>
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<data name="Category" value="Schemas"/>
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</metadata>
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</prolog>
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<conbody>
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<p>
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<indexterm audience="hidden">DESCRIBE statement</indexterm>
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The <codeph>DESCRIBE</codeph> statement displays metadata about a table, such as the column names and their
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data types.
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<ph rev="2.3.0">In <keyword keyref="impala23_full"/> and higher, you can specify the name of a complex type column, which takes
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the form of a dotted path. The path might include multiple components in the case of a nested type definition.</ph>
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<ph rev="2.5.0">In <keyword keyref="impala25_full"/> and higher, the <codeph>DESCRIBE DATABASE</codeph> form can display
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information about a database.</ph>
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</p>
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<p conref="../shared/impala_common.xml#common/syntax_blurb"/>
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<codeblock rev="2.5.0">DESCRIBE [DATABASE] [FORMATTED|EXTENDED] <varname>object_name</varname>
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object_name ::=
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[<varname>db_name</varname>.]<varname>table_name</varname>[.<varname>complex_col_name</varname> ...]
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| <varname>db_name</varname>
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</codeblock>
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<p>
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You can use the abbreviation <codeph>DESC</codeph> for the <codeph>DESCRIBE</codeph> statement.
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</p>
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<p rev="1.1">
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The <codeph>DESCRIBE FORMATTED</codeph> variation displays additional information, in a format familiar to
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users of Apache Hive. The extra information includes low-level details such as whether the table is internal
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or external, when it was created, the file format, the location of the data in HDFS, whether the object is a
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table or a view, and (for views) the text of the query from the view definition.
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</p>
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<note>
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The <codeph>Compressed</codeph> field is not a reliable indicator of whether the table contains compressed
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data. It typically always shows <codeph>No</codeph>, because the compression settings only apply during the
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session that loads data and are not stored persistently with the table metadata.
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</note>
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<p rev="2.5.0 IMPALA-2196">
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<b>Describing databases:</b>
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</p>
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<p rev="2.5.0">
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By default, the <codeph>DESCRIBE</codeph> output for a database includes the location
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and the comment, which can be set by the <codeph>LOCATION</codeph> and <codeph>COMMENT</codeph>
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clauses on the <codeph>CREATE DATABASE</codeph> statement.
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</p>
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<p rev="2.5.0">
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The additional information displayed by the <codeph>FORMATTED</codeph> or <codeph>EXTENDED</codeph>
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keyword includes the HDFS user ID that is considered the owner of the database, and any
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optional database properties. The properties could be specified by the <codeph>WITH DBPROPERTIES</codeph>
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clause if the database is created using a Hive <codeph>CREATE DATABASE</codeph> statement.
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Impala currently does not set or do any special processing based on those properties.
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</p>
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<p rev="2.5.0">
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The following examples show the variations in syntax and output for
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describing databases. This feature is available in <keyword keyref="impala25_full"/>
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and higher.
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</p>
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<codeblock rev="2.5.0">
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describe database default;
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+---------+----------------------+-----------------------+
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| name | location | comment |
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+---------+----------------------+-----------------------+
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| default | /user/hive/warehouse | Default Hive database |
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+---------+----------------------+-----------------------+
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describe database formatted default;
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+---------+----------------------+-----------------------+
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| name | location | comment |
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+---------+----------------------+-----------------------+
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| default | /user/hive/warehouse | Default Hive database |
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| Owner: | | |
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| | public | ROLE |
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+---------+----------------------+-----------------------+
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describe database extended default;
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+---------+----------------------+-----------------------+
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| name | location | comment |
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+---------+----------------------+-----------------------+
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| default | /user/hive/warehouse | Default Hive database |
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| Owner: | | |
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| | public | ROLE |
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+---------+----------------------+-----------------------+
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</codeblock>
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<p>
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<b>Describing tables:</b>
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</p>
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<p>
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If the <codeph>DATABASE</codeph> keyword is omitted, the default
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for the <codeph>DESCRIBE</codeph> statement is to refer to a table.
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</p>
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<p>
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If you have the <codeph>SELECT</codeph> privilege on a subset of the table
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columns and no other relevant table/database/server-level privileges,
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<codeph>DESCRIBE</codeph> returns the data from the columns you have
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access to.
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</p>
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<p>
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If you have the <codeph>SELECT</codeph> privilege on a subset of the table
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columns and no other relevant table/database/server-level privileges,
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<codeph>DESCRIBE FORMATTED/EXTENDED</codeph> does not return
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the <codeph>LOCATION</codeph> field. The <codeph>LOCATION</codeph> data
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is shown if you have any privilege on the table, the containing database
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or the server.
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</p>
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<codeblock>
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-- By default, the table is assumed to be in the current database.
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describe my_table;
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+------+--------+---------+
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| name | type | comment |
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+------+--------+---------+
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| x | int | |
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| s | string | |
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+------+--------+---------+
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-- Use a fully qualified table name to specify a table in any database.
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describe my_database.my_table;
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+------+--------+---------+
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| name | type | comment |
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+------+--------+---------+
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| x | int | |
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| s | string | |
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+------+--------+---------+
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-- The formatted or extended output includes additional useful information.
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-- The LOCATION field is especially useful to know for DDL statements and HDFS commands
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-- during ETL jobs. (The LOCATION includes a full hdfs:// URL, omitted here for readability.)
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describe formatted my_table;
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+------------------------------+----------------------------------------------+----------------------+
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| name | type | comment |
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+------------------------------+----------------------------------------------+----------------------+
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| # col_name | data_type | comment |
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| | NULL | NULL |
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| x | int | NULL |
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| s | string | NULL |
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| | NULL | NULL |
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| # Detailed Table Information | NULL | NULL |
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| Database: | my_database | NULL |
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| Owner: | jrussell | NULL |
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| CreateTime: | Fri Mar 18 15:58:00 PDT 2016 | NULL |
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| LastAccessTime: | UNKNOWN | NULL |
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| Protect Mode: | None | NULL |
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| Retention: | 0 | NULL |
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| Location: | /user/hive/warehouse/my_database.db/my_table | NULL |
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| Table Type: | MANAGED_TABLE | NULL |
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| Table Parameters: | NULL | NULL |
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| | transient_lastDdlTime | 1458341880 |
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| | NULL | NULL |
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| # Storage Information | NULL | NULL |
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| SerDe Library: | org. ... .LazySimpleSerDe | NULL |
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| InputFormat: | org.apache.hadoop.mapred.TextInputFormat | NULL |
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| OutputFormat: | org. ... .HiveIgnoreKeyTextOutputFormat | NULL |
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| Compressed: | No | NULL |
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| Num Buckets: | 0 | NULL |
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| Bucket Columns: | [] | NULL |
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| Sort Columns: | [] | NULL |
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+------------------------------+----------------------------------------------+----------------------+
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</codeblock>
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<p conref="../shared/impala_common.xml#common/complex_types_blurb"/>
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<p rev="2.3.0">
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Because the column definitions for complex types can become long, particularly when such types are nested,
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the <codeph>DESCRIBE</codeph> statement uses special formatting for complex type columns to make the output readable.
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</p>
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<p rev="2.3.0">
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For the <codeph>ARRAY</codeph>, <codeph>STRUCT</codeph>, and <codeph>MAP</codeph> types available in
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<keyword keyref="impala23_full"/> and higher, the <codeph>DESCRIBE</codeph> output is formatted to avoid
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excessively long lines for multiple fields within a <codeph>STRUCT</codeph>, or a nested sequence of
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complex types.
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</p>
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<p conref="../shared/impala_common.xml#common/complex_types_describe"/>
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<p rev="2.3.0">
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For example, here is the <codeph>DESCRIBE</codeph> output for a table containing a single top-level column
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of each complex type:
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</p>
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<codeblock rev="2.3.0"><![CDATA[create table t1 (x int, a array<int>, s struct<f1: string, f2: bigint>, m map<string,int>) stored as parquet;
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describe t1;
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+------+-----------------+---------+
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| name | type | comment |
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+------+-----------------+---------+
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| x | int | |
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| a | array<int> | |
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| s | struct< | |
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| | f1:string, | |
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| | f2:bigint | |
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| | > | |
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| m | map<string,int> | |
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+------+-----------------+---------+
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]]>
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</codeblock>
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<p rev="2.3.0">
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Here are examples showing how to <q>drill down</q> into the layouts of complex types, including
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using multi-part names to examine the definitions of nested types.
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The <codeph>< ></codeph> delimiters identify the columns with complex types;
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these are the columns where you can descend another level to see the parts that make up
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the complex type.
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This technique helps you to understand the multi-part names you use as table references in queries
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involving complex types, and the corresponding column names you refer to in the <codeph>SELECT</codeph> list.
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These tables are from the <q>nested TPC-H</q> schema, shown in detail in
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<xref href="impala_complex_types.xml#complex_sample_schema"/>.
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</p>
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<p>
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The <codeph>REGION</codeph> table contains an <codeph>ARRAY</codeph> of <codeph>STRUCT</codeph>
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elements:
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</p>
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<ul>
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<li>
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<p>
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The first <codeph>DESCRIBE</codeph> specifies the table name, to display the definition
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of each top-level column.
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</p>
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</li>
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<li>
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<p>
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The second <codeph>DESCRIBE</codeph> specifies the name of a complex
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column, <codeph>REGION.R_NATIONS</codeph>, showing that when you include the name of an <codeph>ARRAY</codeph>
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column in a <codeph>FROM</codeph> clause, that table reference acts like a two-column table with
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columns <codeph>ITEM</codeph> and <codeph>POS</codeph>.
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</p>
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</li>
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<li>
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<p>
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The final <codeph>DESCRIBE</codeph> specifies the fully qualified name of the <codeph>ITEM</codeph> field,
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to display the layout of its underlying <codeph>STRUCT</codeph> type in table format, with the fields
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mapped to column names.
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</p>
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</li>
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</ul>
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<codeblock rev="2.3.0"><![CDATA[
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-- #1: The overall layout of the entire table.
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describe region;
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+-------------+-------------------------+---------+
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| name | type | comment |
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+-------------+-------------------------+---------+
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| r_regionkey | smallint | |
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| r_name | string | |
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| r_comment | string | |
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| r_nations | array<struct< | |
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| | n_nationkey:smallint, | |
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| | n_name:string, | |
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| | n_comment:string | |
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| | >> | |
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+-------------+-------------------------+---------+
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-- #2: The ARRAY column within the table.
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describe region.r_nations;
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+------+-------------------------+---------+
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| name | type | comment |
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+------+-------------------------+---------+
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| item | struct< | |
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| | n_nationkey:smallint, | |
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| | n_name:string, | |
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| | n_comment:string | |
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| | > | |
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| pos | bigint | |
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+------+-------------------------+---------+
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-- #3: The STRUCT that makes up each ARRAY element.
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-- The fields of the STRUCT act like columns of a table.
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describe region.r_nations.item;
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+-------------+----------+---------+
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| name | type | comment |
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+-------------+----------+---------+
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| n_nationkey | smallint | |
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| n_name | string | |
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| n_comment | string | |
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+-------------+----------+---------+
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]]>
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</codeblock>
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<p>
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The <codeph>CUSTOMER</codeph> table contains an <codeph>ARRAY</codeph> of <codeph>STRUCT</codeph>
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elements, where one field in the <codeph>STRUCT</codeph> is another <codeph>ARRAY</codeph> of
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<codeph>STRUCT</codeph> elements:
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</p>
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<ul>
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<li>
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<p>
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Again, the initial <codeph>DESCRIBE</codeph> specifies only the table name.
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</p>
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</li>
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<li>
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<p>
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The second <codeph>DESCRIBE</codeph> specifies the qualified name of the complex
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column, <codeph>CUSTOMER.C_ORDERS</codeph>, showing how an <codeph>ARRAY</codeph>
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is represented as a two-column table with columns <codeph>ITEM</codeph> and <codeph>POS</codeph>.
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</p>
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</li>
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<li>
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<p>
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The third <codeph>DESCRIBE</codeph> specifies the qualified name of the <codeph>ITEM</codeph>
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of the <codeph>ARRAY</codeph> column, to see the structure of the nested <codeph>ARRAY</codeph>.
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Again, it has has two parts, <codeph>ITEM</codeph> and <codeph>POS</codeph>. Because the
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<codeph>ARRAY</codeph> contains a <codeph>STRUCT</codeph>, the layout of the <codeph>STRUCT</codeph>
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is shown.
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</p>
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</li>
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<li>
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<p>
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The fourth and fifth <codeph>DESCRIBE</codeph> statements drill down into a <codeph>STRUCT</codeph> field that
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is itself a complex type, an <codeph>ARRAY</codeph> of <codeph>STRUCT</codeph>.
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The <codeph>ITEM</codeph> portion of the qualified name is only required when the <codeph>ARRAY</codeph>
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elements are anonymous. The fields of the <codeph>STRUCT</codeph> give names to any other complex types
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nested inside the <codeph>STRUCT</codeph>. Therefore, the <codeph>DESCRIBE</codeph> parameters
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<codeph>CUSTOMER.C_ORDERS.ITEM.O_LINEITEMS</codeph> and <codeph>CUSTOMER.C_ORDERS.O_LINEITEMS</codeph>
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are equivalent. (For brevity, leave out the <codeph>ITEM</codeph> portion of
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a qualified name when it is not required.)
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</p>
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</li>
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<li>
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<p>
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The final <codeph>DESCRIBE</codeph> shows the layout of the deeply nested <codeph>STRUCT</codeph> type.
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Because there are no more complex types nested inside this <codeph>STRUCT</codeph>, this is as far
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as you can drill down into the layout for this table.
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</p>
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</li>
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</ul>
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<codeblock rev="2.3.0"><![CDATA[-- #1: The overall layout of the entire table.
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describe customer;
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+--------------+------------------------------------+
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| name | type |
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+--------------+------------------------------------+
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| c_custkey | bigint |
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... more scalar columns ...
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| c_orders | array<struct< |
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| | o_orderkey:bigint, |
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| | o_orderstatus:string, |
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| | o_totalprice:decimal(12,2), |
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| | o_orderdate:string, |
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| | o_orderpriority:string, |
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| | o_clerk:string, |
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| | o_shippriority:int, |
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| | o_comment:string, |
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| | o_lineitems:array<struct< |
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| | l_partkey:bigint, |
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| | l_suppkey:bigint, |
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| | l_linenumber:int, |
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| | l_quantity:decimal(12,2), |
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| | l_extendedprice:decimal(12,2), |
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| | l_discount:decimal(12,2), |
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| | l_tax:decimal(12,2), |
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| | l_returnflag:string, |
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| | l_linestatus:string, |
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| | l_shipdate:string, |
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| | l_commitdate:string, |
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| | l_receiptdate:string, |
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| | l_shipinstruct:string, |
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| | l_shipmode:string, |
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| | l_comment:string |
|
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| | >> |
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| | >> |
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+--------------+------------------------------------+
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-- #2: The ARRAY column within the table.
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describe customer.c_orders;
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+------+------------------------------------+
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| name | type |
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+------+------------------------------------+
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| item | struct< |
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| | o_orderkey:bigint, |
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| | o_orderstatus:string, |
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... more struct fields ...
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| | o_lineitems:array<struct< |
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| | l_partkey:bigint, |
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| | l_suppkey:bigint, |
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... more nested struct fields ...
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| | l_comment:string |
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| | >> |
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| | > |
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| pos | bigint |
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+------+------------------------------------+
|
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-- #3: The STRUCT that makes up each ARRAY element.
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-- The fields of the STRUCT act like columns of a table.
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describe customer.c_orders.item;
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+-----------------+----------------------------------+
|
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| name | type |
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+-----------------+----------------------------------+
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| o_orderkey | bigint |
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| o_orderstatus | string |
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| o_totalprice | decimal(12,2) |
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| o_orderdate | string |
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| o_orderpriority | string |
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| o_clerk | string |
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| o_shippriority | int |
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| o_comment | string |
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| o_lineitems | array<struct< |
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| | l_partkey:bigint, |
|
|
| | l_suppkey:bigint, |
|
|
... more struct fields ...
|
|
| | l_comment:string |
|
|
| | >> |
|
|
+-----------------+----------------------------------+
|
|
|
|
-- #4: The ARRAY nested inside the STRUCT elements of the first ARRAY.
|
|
describe customer.c_orders.item.o_lineitems;
|
|
+------+----------------------------------+
|
|
| name | type |
|
|
+------+----------------------------------+
|
|
| item | struct< |
|
|
| | l_partkey:bigint, |
|
|
| | l_suppkey:bigint, |
|
|
... more struct fields ...
|
|
| | l_comment:string |
|
|
| | > |
|
|
| pos | bigint |
|
|
+------+----------------------------------+
|
|
|
|
-- #5: Shorter form of the previous DESCRIBE. Omits the .ITEM portion of the name
|
|
-- because O_LINEITEMS and other field names provide a way to refer to things
|
|
-- inside the ARRAY element.
|
|
describe customer.c_orders.o_lineitems;
|
|
+------+----------------------------------+
|
|
| name | type |
|
|
+------+----------------------------------+
|
|
| item | struct< |
|
|
| | l_partkey:bigint, |
|
|
| | l_suppkey:bigint, |
|
|
... more struct fields ...
|
|
| | l_comment:string |
|
|
| | > |
|
|
| pos | bigint |
|
|
+------+----------------------------------+
|
|
|
|
-- #6: The STRUCT representing ARRAY elements nested inside
|
|
-- another ARRAY of STRUCTs. The lack of any complex types
|
|
-- in this output means this is as far as DESCRIBE can
|
|
-- descend into the table layout.
|
|
describe customer.c_orders.o_lineitems.item;
|
|
+-----------------+---------------+
|
|
| name | type |
|
|
+-----------------+---------------+
|
|
| l_partkey | bigint |
|
|
| l_suppkey | bigint |
|
|
... more scalar columns ...
|
|
| l_comment | string |
|
|
+-----------------+---------------+
|
|
]]>
|
|
</codeblock>
|
|
|
|
<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
|
|
|
|
<p>
|
|
After the <cmdname>impalad</cmdname> daemons are restarted, the first query against a table can take longer
|
|
than subsequent queries, because the metadata for the table is loaded before the query is processed. This
|
|
one-time delay for each table can cause misleading results in benchmark tests or cause unnecessary concern.
|
|
To <q>warm up</q> the Impala metadata cache, you can issue a <codeph>DESCRIBE</codeph> statement in advance
|
|
for each table you intend to access later.
|
|
</p>
|
|
|
|
<p>
|
|
When you are dealing with data files stored in HDFS, sometimes it is important to know details such as the
|
|
path of the data files for an Impala table, and the hostname for the namenode. You can get this information
|
|
from the <codeph>DESCRIBE FORMATTED</codeph> output. You specify HDFS URIs or path specifications with
|
|
statements such as <codeph>LOAD DATA</codeph> and the <codeph>LOCATION</codeph> clause of <codeph>CREATE
|
|
TABLE</codeph> or <codeph>ALTER TABLE</codeph>. You might also use HDFS URIs or paths with Linux commands
|
|
such as <cmdname>hadoop</cmdname> and <cmdname>hdfs</cmdname> to copy, rename, and so on, data files in HDFS.
|
|
</p>
|
|
|
|
<p conref="../shared/impala_common.xml#common/sync_ddl_blurb"/>
|
|
|
|
<p rev="1.2.1">
|
|
Each table can also have associated table statistics and column statistics. To see these categories of
|
|
information, use the <codeph>SHOW TABLE STATS <varname>table_name</varname></codeph> and <codeph>SHOW COLUMN
|
|
STATS <varname>table_name</varname></codeph> statements.
|
|
<!--
|
|
For example, the table statistics can often show you the number
|
|
and total size of the files in the table, even if you have not
|
|
run <codeph>COMPUTE STATS</codeph>.
|
|
-->
|
|
See <xref href="impala_show.xml#show"/> for details.
|
|
</p>
|
|
|
|
<note conref="../shared/impala_common.xml#common/compute_stats_next"/>
|
|
|
|
<p conref="../shared/impala_common.xml#common/example_blurb"/>
|
|
|
|
<p>
|
|
The following example shows the results of both a standard <codeph>DESCRIBE</codeph> and <codeph>DESCRIBE
|
|
FORMATTED</codeph> for different kinds of schema objects:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<codeph>DESCRIBE</codeph> for a table or a view returns the name, type, and comment for each of the
|
|
columns. For a view, if the column value is computed by an expression, the column name is automatically
|
|
generated as <codeph>_c0</codeph>, <codeph>_c1</codeph>, and so on depending on the ordinal number of the
|
|
column.
|
|
</li>
|
|
|
|
<li>
|
|
A table created with no special format or storage clauses is designated as a <codeph>MANAGED_TABLE</codeph>
|
|
(an <q>internal table</q> in Impala terminology). Its data files are stored in an HDFS directory under the
|
|
default Hive data directory. By default, it uses Text data format.
|
|
</li>
|
|
|
|
<li>
|
|
A view is designated as <codeph>VIRTUAL_VIEW</codeph> in <codeph>DESCRIBE FORMATTED</codeph> output. Some
|
|
of its properties are <codeph>NULL</codeph> or blank because they are inherited from the base table. The
|
|
text of the query that defines the view is part of the <codeph>DESCRIBE FORMATTED</codeph> output.
|
|
</li>
|
|
|
|
<li>
|
|
A table with additional clauses in the <codeph>CREATE TABLE</codeph> statement has differences in
|
|
<codeph>DESCRIBE FORMATTED</codeph> output. The output for <codeph>T2</codeph> includes the
|
|
<codeph>EXTERNAL_TABLE</codeph> keyword because of the <codeph>CREATE EXTERNAL TABLE</codeph> syntax, and
|
|
different <codeph>InputFormat</codeph> and <codeph>OutputFormat</codeph> fields to reflect the Parquet file
|
|
format.
|
|
</li>
|
|
</ul>
|
|
|
|
<codeblock>[localhost:21000] > create table t1 (x int, y int, s string);
|
|
Query: create table t1 (x int, y int, s string)
|
|
[localhost:21000] > describe t1;
|
|
Query: describe t1
|
|
Query finished, fetching results ...
|
|
+------+--------+---------+
|
|
| name | type | comment |
|
|
+------+--------+---------+
|
|
| x | int | |
|
|
| y | int | |
|
|
| s | string | |
|
|
+------+--------+---------+
|
|
Returned 3 row(s) in 0.13s
|
|
[localhost:21000] > describe formatted t1;
|
|
Query: describe formatted t1
|
|
Query finished, fetching results ...
|
|
+------------------------------+--------------------------------------------+------------+
|
|
| name | type | comment |
|
|
+------------------------------+--------------------------------------------+------------+
|
|
| # col_name | data_type | comment |
|
|
| | NULL | NULL |
|
|
| x | int | None |
|
|
| y | int | None |
|
|
| s | string | None |
|
|
| | NULL | NULL |
|
|
| # Detailed Table Information | NULL | NULL |
|
|
| Database: | describe_formatted | NULL |
|
|
| Owner: | doc_demo | NULL |
|
|
| CreateTime: | Mon Jul 22 17:03:16 EDT 2013 | NULL |
|
|
| LastAccessTime: | UNKNOWN | NULL |
|
|
| Protect Mode: | None | NULL |
|
|
| Retention: | 0 | NULL |
|
|
| Location: | hdfs://127.0.0.1:8020/user/hive/warehouse/ | |
|
|
| | describe_formatted.db/t1 | NULL |
|
|
| Table Type: | MANAGED_TABLE | NULL |
|
|
| Table Parameters: | NULL | NULL |
|
|
| | transient_lastDdlTime | 1374526996 |
|
|
| | NULL | NULL |
|
|
| # Storage Information | NULL | NULL |
|
|
| SerDe Library: | org.apache.hadoop.hive.serde2.lazy. | |
|
|
| | LazySimpleSerDe | NULL |
|
|
| InputFormat: | org.apache.hadoop.mapred.TextInputFormat | NULL |
|
|
| OutputFormat: | org.apache.hadoop.hive.ql.io. | |
|
|
| | HiveIgnoreKeyTextOutputFormat | NULL |
|
|
| Compressed: | No | NULL |
|
|
| Num Buckets: | 0 | NULL |
|
|
| Bucket Columns: | [] | NULL |
|
|
| Sort Columns: | [] | NULL |
|
|
+------------------------------+--------------------------------------------+------------+
|
|
Returned 26 row(s) in 0.03s
|
|
[localhost:21000] > create view v1 as select x, upper(s) from t1;
|
|
Query: create view v1 as select x, upper(s) from t1
|
|
[localhost:21000] > describe v1;
|
|
Query: describe v1
|
|
Query finished, fetching results ...
|
|
+------+--------+---------+
|
|
| name | type | comment |
|
|
+------+--------+---------+
|
|
| x | int | |
|
|
| _c1 | string | |
|
|
+------+--------+---------+
|
|
Returned 2 row(s) in 0.10s
|
|
[localhost:21000] > describe formatted v1;
|
|
Query: describe formatted v1
|
|
Query finished, fetching results ...
|
|
+------------------------------+------------------------------+----------------------+
|
|
| name | type | comment |
|
|
+------------------------------+------------------------------+----------------------+
|
|
| # col_name | data_type | comment |
|
|
| | NULL | NULL |
|
|
| x | int | None |
|
|
| _c1 | string | None |
|
|
| | NULL | NULL |
|
|
| # Detailed Table Information | NULL | NULL |
|
|
| Database: | describe_formatted | NULL |
|
|
| Owner: | doc_demo | NULL |
|
|
| CreateTime: | Mon Jul 22 16:56:38 EDT 2013 | NULL |
|
|
| LastAccessTime: | UNKNOWN | NULL |
|
|
| Protect Mode: | None | NULL |
|
|
| Retention: | 0 | NULL |
|
|
| Table Type: | VIRTUAL_VIEW | NULL |
|
|
| Table Parameters: | NULL | NULL |
|
|
| | transient_lastDdlTime | 1374526598 |
|
|
| | NULL | NULL |
|
|
| # Storage Information | NULL | NULL |
|
|
| SerDe Library: | null | NULL |
|
|
| InputFormat: | null | NULL |
|
|
| OutputFormat: | null | NULL |
|
|
| Compressed: | No | NULL |
|
|
| Num Buckets: | 0 | NULL |
|
|
| Bucket Columns: | [] | NULL |
|
|
| Sort Columns: | [] | NULL |
|
|
| | NULL | NULL |
|
|
| # View Information | NULL | NULL |
|
|
| View Original Text: | SELECT x, upper(s) FROM t1 | NULL |
|
|
| View Expanded Text: | SELECT x, upper(s) FROM t1 | NULL |
|
|
+------------------------------+------------------------------+----------------------+
|
|
Returned 28 row(s) in 0.03s
|
|
[localhost:21000] > create external table t2 (x int, y int, s string) stored as parquet location '/user/doc_demo/sample_data';
|
|
[localhost:21000] > describe formatted t2;
|
|
Query: describe formatted t2
|
|
Query finished, fetching results ...
|
|
+------------------------------+----------------------------------------------------+------------+
|
|
| name | type | comment |
|
|
+------------------------------+----------------------------------------------------+------------+
|
|
| # col_name | data_type | comment |
|
|
| | NULL | NULL |
|
|
| x | int | None |
|
|
| y | int | None |
|
|
| s | string | None |
|
|
| | NULL | NULL |
|
|
| # Detailed Table Information | NULL | NULL |
|
|
| Database: | describe_formatted | NULL |
|
|
| Owner: | doc_demo | NULL |
|
|
| CreateTime: | Mon Jul 22 17:01:47 EDT 2013 | NULL |
|
|
| LastAccessTime: | UNKNOWN | NULL |
|
|
| Protect Mode: | None | NULL |
|
|
| Retention: | 0 | NULL |
|
|
| Location: | hdfs://127.0.0.1:8020/user/doc_demo/sample_data | NULL |
|
|
| Table Type: | EXTERNAL_TABLE | NULL |
|
|
| Table Parameters: | NULL | NULL |
|
|
| | EXTERNAL | TRUE |
|
|
| | transient_lastDdlTime | 1374526907 |
|
|
| | NULL | NULL |
|
|
| # Storage Information | NULL | NULL |
|
|
| SerDe Library: | org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe | NULL |
|
|
| InputFormat: | org.apache.impala.hive.serde.ParquetInputFormat | NULL |
|
|
| OutputFormat: | org.apache.impala.hive.serde.ParquetOutputFormat | NULL |
|
|
| Compressed: | No | NULL |
|
|
| Num Buckets: | 0 | NULL |
|
|
| Bucket Columns: | [] | NULL |
|
|
| Sort Columns: | [] | NULL |
|
|
+------------------------------+----------------------------------------------------+------------+
|
|
Returned 27 row(s) in 0.17s</codeblock>
|
|
|
|
<p conref="../shared/impala_common.xml#common/cancel_blurb_no"/>
|
|
|
|
<p conref="../shared/impala_common.xml#common/permissions_blurb"/>
|
|
<p rev="">
|
|
The user ID that the <cmdname>impalad</cmdname> daemon runs under,
|
|
typically the <codeph>impala</codeph> user, must have read and execute
|
|
permissions for all directories that are part of the table.
|
|
(A table could span multiple different HDFS directories if it is partitioned.
|
|
The directories could be widely scattered because a partition can reside
|
|
in an arbitrary HDFS directory based on its <codeph>LOCATION</codeph> attribute.)
|
|
</p>
|
|
|
|
<p rev="kudu" conref="../shared/impala_common.xml#common/kudu_blurb"/>
|
|
|
|
<p rev="kudu">
|
|
The information displayed for Kudu tables includes the additional attributes
|
|
that are only applicable for Kudu tables:
|
|
</p>
|
|
<ul rev="kudu">
|
|
<li>
|
|
Whether or not the column is part of the primary key. Every Kudu table
|
|
has a <codeph>true</codeph> value here for at least one column. There
|
|
could be multiple <codeph>true</codeph> values, for tables with
|
|
composite primary keys.
|
|
</li>
|
|
<li>
|
|
Whether or not the column is nullable. Specified by the <codeph>NULL</codeph>
|
|
or <codeph>NOT NULL</codeph> attributes on the <codeph>CREATE TABLE</codeph> statement.
|
|
Columns that are part of the primary key are automatically non-nullable.
|
|
</li>
|
|
<li>
|
|
The default value, if any, for the column. Specified by the <codeph>DEFAULT</codeph>
|
|
attribute on the <codeph>CREATE TABLE</codeph> statement. If the default value is
|
|
<codeph>NULL</codeph>, that is not indicated in this column. It is implied by
|
|
<codeph>nullable</codeph> being true and no other default value specified.
|
|
</li>
|
|
<li>
|
|
The encoding used for values in the column. Specified by the <codeph>ENCODING</codeph>
|
|
attribute on the <codeph>CREATE TABLE</codeph> statement.
|
|
</li>
|
|
<li>
|
|
The compression used for values in the column. Specified by the <codeph>COMPRESSION</codeph>
|
|
attribute on the <codeph>CREATE TABLE</codeph> statement.
|
|
</li>
|
|
<li>
|
|
The block size (in bytes) used for the underlying Kudu storage layer for the column.
|
|
Specified by the <codeph>BLOCK_SIZE</codeph> attribute on the <codeph>CREATE TABLE</codeph>
|
|
statement.
|
|
</li>
|
|
</ul>
|
|
|
|
<p rev="kudu">
|
|
The following example shows <codeph>DESCRIBE</codeph> output for a simple Kudu table, with
|
|
a single-column primary key and all column attributes left with their default values:
|
|
</p>
|
|
|
|
<codeblock rev="kudu">
|
|
describe million_rows;
|
|
+------+--------+---------+-------------+----------+---------------+---------------+---------------------+------------+
|
|
| name | type | comment | primary_key | nullable | default_value | encoding | compression | block_size |
|
|
+------+--------+---------+-------------+----------+---------------+---------------+---------------------+------------+
|
|
| id | string | | true | false | | AUTO_ENCODING | DEFAULT_COMPRESSION | 0 |
|
|
| s | string | | false | false | | AUTO_ENCODING | DEFAULT_COMPRESSION | 0 |
|
|
+------+--------+---------+-------------+----------+---------------+---------------+---------------------+------------+
|
|
</codeblock>
|
|
|
|
<p rev="kudu">
|
|
The following example shows <codeph>DESCRIBE</codeph> output for a Kudu table with a
|
|
two-column primary key, and Kudu-specific attributes applied to some columns:
|
|
</p>
|
|
|
|
<codeblock rev="kudu">
|
|
create table kudu_describe_example
|
|
(
|
|
c1 int, c2 int,
|
|
c3 string, c4 string not null, c5 string default 'n/a', c6 string default '',
|
|
c7 bigint not null, c8 bigint null default null, c9 bigint default -1 encoding bit_shuffle,
|
|
primary key(c1,c2)
|
|
)
|
|
partition by hash (c1, c2) partitions 10 stored as kudu;
|
|
|
|
describe kudu_describe_example;
|
|
+------+--------+---------+-------------+----------+---------------+---------------+---------------------+------------+
|
|
| name | type | comment | primary_key | nullable | default_value | encoding | compression | block_size |
|
|
+------+--------+---------+-------------+----------+---------------+---------------+---------------------+------------+
|
|
| c1 | int | | true | false | | AUTO_ENCODING | DEFAULT_COMPRESSION | 0 |
|
|
| c2 | int | | true | false | | AUTO_ENCODING | DEFAULT_COMPRESSION | 0 |
|
|
| c3 | string | | false | true | | AUTO_ENCODING | DEFAULT_COMPRESSION | 0 |
|
|
| c4 | string | | false | false | | AUTO_ENCODING | DEFAULT_COMPRESSION | 0 |
|
|
| c5 | string | | false | true | n/a | AUTO_ENCODING | DEFAULT_COMPRESSION | 0 |
|
|
| c6 | string | | false | true | | AUTO_ENCODING | DEFAULT_COMPRESSION | 0 |
|
|
| c7 | bigint | | false | false | | AUTO_ENCODING | DEFAULT_COMPRESSION | 0 |
|
|
| c8 | bigint | | false | true | | AUTO_ENCODING | DEFAULT_COMPRESSION | 0 |
|
|
| c9 | bigint | | false | true | -1 | BIT_SHUFFLE | DEFAULT_COMPRESSION | 0 |
|
|
+------+--------+---------+-------------+----------+---------------+---------------+---------------------+------------+
|
|
</codeblock>
|
|
|
|
<p conref="../shared/impala_common.xml#common/related_info"/>
|
|
|
|
<p>
|
|
<xref href="impala_tables.xml#tables"/>, <xref href="impala_create_table.xml#create_table"/>,
|
|
<xref href="impala_show.xml#show_tables"/>, <xref href="impala_show.xml#show_create_table"/>
|
|
</p>
|
|
</conbody>
|
|
</concept>
|