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spark-instrumented-optimizer/docs/sql-ref-syntax-aux-describe-table.md
Takeshi Yamamuro 179289f0bf [SPARK-31383][SQL][DOC] Clean up the SQL documents in docs/sql-ref* 
### What changes were proposed in this pull request?

This PR intends to clean up the SQL documents in `doc/sql-ref*`.
Main changes are as follows;

 - Fixes wrong syntaxes and capitalize sub-titles
 - Adds some DDL queries in `Examples` so that users can run examples there
 - Makes query output in `Examples` follows the `Dataset.showString` (right-aligned) format
 - Adds/Removes spaces, Indents, or blank lines to follow the format below;

```
---
license...
---

### Description

Writes what's the syntax is.

### Syntax

{% highlight sql %}
SELECT...
    WHERE... // 4 indents after the second line
    ...
{% endhighlight %}

### Parameters

<dl>

  <dt><code><em>Param Name</em></code></dt>
  <dd>
    Param Description
  </dd>
  ...
</dl>

### Examples

{% highlight sql %}
-- It is better that users are able to execute example queries here.
-- So, we prepare test data in the first section if possible.
CREATE TABLE t (key STRING, value DOUBLE);
INSERT INTO t VALUES
    ('a', 1.0), ('a', 2.0), ('b', 3.0), ('c', 4.0);

-- query output has 2 indents and it follows the `Dataset.showString`
-- format (right-aligned).
SELECT * FROM t;
  +---+-----+
  |key|value|
  +---+-----+
  |  a|  1.0|
  |  a|  2.0|
  |  b|  3.0|
  |  c|  4.0|
  +---+-----+

-- Query statements after the second line have 4 indents.
SELECT key, SUM(value)
    FROM t
    GROUP BY key;
  +---+----------+
  |key|sum(value)|
  +---+----------+
  |  c|       4.0|
  |  b|       3.0|
  |  a|       3.0|
  +---+----------+
...
{% endhighlight %}

### Related Statements

 * [XXX](xxx.html)
 * ...
```

### Why are the changes needed?

The most changes of this PR are pretty minor, but I think the consistent formats/rules to write documents are important for long-term maintenance in our community

### Does this PR introduce any user-facing change?

Yes.

### How was this patch tested?

Manually checked.

Closes #28151 from maropu/MakeRightAligned.

Authored-by: Takeshi Yamamuro <yamamuro@apache.org>
Signed-off-by: Sean Owen <srowen@gmail.com>
2020-04-12 23:40:36 -05:00

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---
layout: global
title: DESCRIBE TABLE
displayTitle: DESCRIBE TABLE
license: |
Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements. See the NOTICE file distributed with
this work for additional information regarding copyright ownership.
The ASF licenses this file to You under the Apache License, Version 2.0
(the "License"); you may not use this file except in compliance with
the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
---
### Description
`DESCRIBE TABLE` statement returns the basic metadata information of a
table. The metadata information includes column name, column type
and column comment. Optionally a partition spec or column name may be specified
to return the metadata pertaining to a partition or column respectively.
### Syntax
{% highlight sql %}
{ DESC | DESCRIBE } [ TABLE ] [ format ] table_identifier [ partition_spec ] [ col_name ]
{% endhighlight %}
### Parameters
<dl>
<dt><code><em>format</em></code></dt>
<dd>
Specifies the optional format of describe output. If `EXTENDED` is specified
then additional metadata information (such as parent database, owner, and access time)
is returned.
</dd>
<dt><code><em>table_identifier</em></code></dt>
<dd>
Specifies a table name, which may be optionally qualified with a database name.<br><br>
<b>Syntax:</b>
<code>
[ database_name. ] table_name
</code>
</dd>
<dt><code><em>partition_spec</em></code></dt>
<dd>
An optional parameter that specifies a comma separated list of key and value pairs
for partitions. When specified, additional partition metadata is returned.<br><br>
<b>Syntax:</b>
<code>
PARTITION ( partition_col_name = partition_col_val [ , ... ] )
</code>
</dd>
<dt><code><em>col_name</em></code></dt>
<dd>
An optional parameter that specifies the column name that needs to be described.
The supplied column name may be optionally qualified. Parameters `partition_spec`
and `col_name` are mutually exclusive and can not be specified together. Currently
nested columns are not allowed to be specified.<br><br>
<b>Syntax:</b>
<code>
[ database_name. ] [ table_name. ] column_name
</code>
</dd>
</dl>
### Examples
{% highlight sql %}
-- Creates a table `customer`. Assumes current database is `salesdb`.
CREATE TABLE customer(
cust_id INT,
state VARCHAR(20),
name STRING COMMENT 'Short name'
)
USING parquet
PARTITIONED BY (state);
INSERT INTO customer PARTITION (state = 'AR') VALUES (100, 'Mike');
-- Returns basic metadata information for unqualified table `customer`
DESCRIBE TABLE customer;
+-----------------------+---------+----------+
| col_name|data_type| comment|
+-----------------------+---------+----------+
| cust_id| int| null|
| name| string|Short name|
| state| string| null|
|# Partition Information| | |
| # col_name|data_type| comment|
| state| string| null|
+-----------------------+---------+----------+
-- Returns basic metadata information for qualified table `customer`
DESCRIBE TABLE salesdb.customer;
+-----------------------+---------+----------+
| col_name|data_type| comment|
+-----------------------+---------+----------+
| cust_id| int| null|
| name| string|Short name|
| state| string| null|
|# Partition Information| | |
| # col_name|data_type| comment|
| state| string| null|
+-----------------------+---------+----------+
-- Returns additional metadata such as parent database, owner, access time etc.
DESCRIBE TABLE EXTENDED customer;
+----------------------------+------------------------------+----------+
| col_name| data_type| comment|
+----------------------------+------------------------------+----------+
| cust_id| int| null|
| name| string|Short name|
| state| string| null|
| # Partition Information| | |
| # col_name| data_type| comment|
| state| string| null|
| | | |
|# Detailed Table Information| | |
| Database| default| |
| Table| customer| |
| Owner| <TABLE OWNER>| |
| Created Time| Tue Apr 07 22:56:34 JST 2020| |
| Last Access| UNKNOWN| |
| Created By| <SPARK VERSION>| |
| Type| MANAGED| |
| Provider| parquet| |
| Location|file:/tmp/salesdb.db/custom...| |
| Serde Library|org.apache.hadoop.hive.ql.i...| |
| InputFormat|org.apache.hadoop.hive.ql.i...| |
| OutputFormat|org.apache.hadoop.hive.ql.i...| |
| Partition Provider| Catalog| |
+----------------------------+------------------------------+----------+
-- Returns partition metadata such as partitioning column name, column type and comment.
DESCRIBE TABLE EXTENDED customer PARTITION (state = 'AR');
+------------------------------+------------------------------+----------+
| col_name| data_type| comment|
+------------------------------+------------------------------+----------+
| cust_id| int| null|
| name| string|Short name|
| state| string| null|
| # Partition Information| | |
| # col_name| data_type| comment|
| state| string| null|
| | | |
|# Detailed Partition Inform...| | |
| Database| default| |
| Table| customer| |
| Partition Values| [state=AR]| |
| Location|file:/tmp/salesdb.db/custom...| |
| Serde Library|org.apache.hadoop.hive.ql.i...| |
| InputFormat|org.apache.hadoop.hive.ql.i...| |
| OutputFormat|org.apache.hadoop.hive.ql.i...| |
| Storage Properties|[serialization.format=1, pa...| |
| Partition Parameters|{transient_lastDdlTime=1586...| |
| Created Time| Tue Apr 07 23:05:43 JST 2020| |
| Last Access| UNKNOWN| |
| Partition Statistics| 659 bytes| |
| | | |
| # Storage Information| | |
| Location|file:/tmp/salesdb.db/custom...| |
| Serde Library|org.apache.hadoop.hive.ql.i...| |
| InputFormat|org.apache.hadoop.hive.ql.i...| |
| OutputFormat|org.apache.hadoop.hive.ql.i...| |
+------------------------------+------------------------------+----------+
-- Returns the metadata for `name` column.
-- Optional `TABLE` clause is omitted and column is fully qualified.
DESCRIBE customer salesdb.customer.name;
+---------+----------+
|info_name|info_value|
+---------+----------+
| col_name| name|
|data_type| string|
| comment|Short name|
+---------+----------+
{% endhighlight %}
### Related Statements
* [DESCRIBE DATABASE](sql-ref-syntax-aux-describe-database.html)
* [DESCRIBE QUERY](sql-ref-syntax-aux-describe-query.html)
* [DESCRIBE FUNCTION](sql-ref-syntax-aux-describe-function.html)
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