babefdee1c
### What changes were proposed in this pull request? Standardize sql reference ### Why are the changes needed? To have consistent docs ### Does this PR introduce any user-facing change? Yes ### How was this patch tested? Tested using jykyll build --serve Closes #26721 from huaxingao/spark-30085. Authored-by: Huaxin Gao <huaxing@us.ibm.com> Signed-off-by: Sean Owen <sean.owen@databricks.com>
184 lines
9 KiB
Markdown
184 lines
9 KiB
Markdown
---
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layout: global
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title: DESCRIBE TABLE
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displayTitle: DESCRIBE TABLE
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license: |
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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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, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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---
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### Description
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`DESCRIBE TABLE` statement returns the basic metadata information of a
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table. The metadata information includes column name, column type
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and column comment. Optionally a partition spec or column name may be specified
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to return the metadata pertaining to a partition or column respectively.
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### Syntax
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{% highlight sql %}
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{ DESC | DESCRIBE } [ TABLE ] [ format ] table_identifier [ partition_spec ] [ col_name ]
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{% endhighlight %}
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### Parameters
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<dl>
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<dt><code><em>format</em></code></dt>
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<dd>
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Specifies the optional format of describe output. If `EXTENDED` is specified
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then additional metadata information (such as parent database, owner, and access time)
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is returned.
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</dd>
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<dt><code><em>table_identifier</em></code></dt>
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<dd>
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Specifies a table name, which may be optionally qualified with a database name.<br><br>
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<b>Syntax:</b>
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<code>
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[ database_name. ] table_name
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</code>
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</dd>
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<dt><code><em>partition_spec</em></code></dt>
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<dd>
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An optional parameter that specifies a comma separated list of key and value pairs
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for partitions. When specified, additional partition metadata is returned.<br><br>
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<b>Syntax:</b>
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<code>
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PARTITION ( partition_col_name = partition_col_val [ , ... ] )
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</code>
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</dd>
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<dt><code><em>col_name</em></code></dt>
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<dd>
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An optional parameter that specifies the column name that needs to be described.
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The supplied column name may be optionally qualified. Parameters `partition_spec`
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and `col_name` are mutually exclusive and can not be specified together. Currently
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nested columns are not allowed to be specified.<br><br>
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<b>Syntax:</b>
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<code>
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[ database_name. ] [ table_name. ] column_name
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</code>
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</dd>
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</dl>
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### Examples
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{% highlight sql %}
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-- Creates a table `customer`. Assumes current database is `salesdb`.
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CREATE TABLE customer(
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cust_id INT,
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state VARCHAR(20),
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name STRING COMMENT 'Short name'
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)
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USING parquet
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PARTITION BY state;
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;
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-- Returns basic metadata information for unqualified table `customer`
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DESCRIBE TABLE customer;
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+-----------------------+---------+----------+
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|col_name |data_type|comment |
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+-----------------------+---------+----------+
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|cust_id |int |null |
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|name |string |Short name|
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|state |string |null |
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|# Partition Information| | |
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|# col_name |data_type|comment |
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|state |string |null |
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+-----------------------+---------+----------+
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-- Returns basic metadata information for qualified table `customer`
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DESCRIBE TABLE salesdb.customer;
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+-----------------------+---------+----------+
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|col_name |data_type|comment |
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+-----------------------+---------+----------+
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|cust_id |int |null |
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|name |string |Short name|
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|state |string |null |
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|# Partition Information| | |
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|# col_name |data_type|comment |
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|state |string |null |
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+-----------------------+---------+----------+
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-- Returns additional metadata such as parent database, owner, access time etc.
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DESCRIBE TABLE EXTENDED customer;
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+----------------------------+------------------------------+----------+
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|col_name |data_type |comment |
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+----------------------------+------------------------------+----------+
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|cust_id |int |null |
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|name |string |Short name|
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|state |string |null |
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|# Partition Information | | |
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|# col_name |data_type |comment |
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|state |string |null |
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| | | |
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|# Detailed Table Information| | |
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|Database |salesdb | |
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|Table |customer | |
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|Owner |<table owner> | |
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|Created Time |Fri Aug 30 09:26:04 PDT 2019 | |
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|Last Access |Wed Dec 31 16:00:00 PST 1969 | |
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|Created By |<spark version> | |
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|Type |MANAGED | |
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|Provider |parquet | |
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|Location |file:.../salesdb.db/customer | |
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|Serde Library |...serde.ParquetHiveSerDe | |
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|InputFormat |...MapredParquetInputFormat | |
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|OutputFormat |...MapredParquetOutputFormat | |
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+----------------------------+------------------------------+----------+
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-- Returns partition metadata such as partitioning column name, column type and comment.
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DESCRIBE TABLE customer PARTITION (state = 'AR');
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+--------------------------------+-----------------------------------------+----------+
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|col_name |data_type |comment |
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+--------------------------------+-----------------------------------------+----------+
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|cust_id |int |null |
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|name |string |Short name|
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|state |string |null |
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|# Partition Information | | |
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|# col_name |data_type |comment |
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|state |string |null |
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| | | |
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|# Detailed Partition Information| | |
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|Database |salesdb | |
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|Table |customer | |
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|Partition Values |[state=AR] | |
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|Location |file:.../salesdb.db/customer/state=AR | |
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|Serde Library |...serde.ParquetHiveSerDe | |
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|InputFormat |...parquet.MapredParquetInputFormat | |
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|OutputFormat |...parquet.MapredParquetOutputFormat | |
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|Storage Properties |[path=file:.../salesdb.db/customer, | |
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| | serialization.format=1] | |
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|Partition Parameters |{rawDataSize=-1, numFiles=1l, | |
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| | transient_lastDdlTime=1567185245, | |
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| | totalSize=688, | |
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| | COLUMN_STATS_ACCURATE=false, numRows=-1}| |
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|Created Time |Fri Aug 30 10:14:05 PDT 2019 | |
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|Last Access |Wed Dec 31 16:00:00 PST 1969 | |
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|Partition Statistics |688 bytes | |
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+--------------------------------+-----------------------------------------+----------+
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-- Returns the metadata for `name` column.
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-- Optional `TABLE` clause is omitted and column is fully qualified.
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DESCRIBE customer salesdb.customer.name;
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+---------+----------+
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|info_name|info_value|
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+---------+----------+
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|col_name |name |
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|data_type|string |
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|comment |Short name|
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+---------+----------+
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{% endhighlight %}
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### Related Statements
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- [DESCRIBE DATABASE](sql-ref-syntax-aux-describe-database.html)
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- [DESCRIBE QUERY](sql-ref-syntax-aux-describe-query.html)
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- [DESCRIBE FUNCTION](sql-ref-syntax-aux-describe-function.html)
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