179289f0bf
### 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>
9 KiB
| layout | title | displayTitle | license |
|---|---|---|---|
| global | DESCRIBE TABLE | DESCRIBE TABLE | 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
format- 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.
table_identifier-
Specifies a table name, which may be optionally qualified with a database name.
Syntax:[ database_name. ] table_name partition_spec-
An optional parameter that specifies a comma separated list of key and value pairs
for partitions. When specified, additional partition metadata is returned.
Syntax:PARTITION ( partition_col_name = partition_col_val [ , ... ] ) col_name-
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.
<b>Syntax:</b> <code> [ database_name. ] [ table_name. ] column_name </code>
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| | | | Created Time| Tue Apr 07 22:56:34 JST 2020| | | Last Access| UNKNOWN| | | Created By| | | | 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 %}