spark-instrumented-optimizer/docs/sql-ref-syntax-qry-select-groupby.md at 179289f0bfc183866d635dc72b507902a3452d3a

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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Raw Blame History

layout	title	displayTitle	license
global	GROUP BY Clause	GROUP BY Clause	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

The GROUP BY clause is used to group the rows based on a set of specified grouping expressions and compute aggregations on the group of rows based on one or more specified aggregate functions. Spark also supports advanced aggregations to do multiple aggregations for the same input record set via GROUPING SETS, CUBE, ROLLUP clauses. When a FILTER clause is attached to an aggregate function, only the matching rows are passed to that function.

Syntax

{% highlight sql %} GROUP BY group_expression [ , group_expression [ , ... ] ] [ { WITH ROLLUP | WITH CUBE | GROUPING SETS (grouping_set [ , ...]) } ]

GROUP BY GROUPING SETS (grouping_set [ , ...]) {% endhighlight %}

While aggregate functions are defined as {% highlight sql %} aggregate_name ( [ DISTINCT ] expression [ , ... ] ) [ FILTER ( WHERE boolean_expression ) ] {% endhighlight %}

Parameters

GROUPING SETS: Groups the rows for each subset of the expressions specified in the grouping sets. For example, GROUP BY GROUPING SETS (warehouse, product) is semantically equivalent to union of results of GROUP BY warehouse and GROUP BY product. This clause is a shorthand for a UNION ALL where each leg of the UNION ALL operator performs aggregation of subset of the columns specified in the GROUPING SETS clause.
grouping_set: A grouping set is specified by zero or more comma-separated expressions in parentheses.

Syntax: ([expression [, ...]])
grouping_expression: Specifies the critieria based on which the rows are grouped together. The grouping of rows is performed based on result values of the grouping expressions. A grouping expression may be a column alias, a column position or an expression.
ROLLUP: Specifies multiple levels of aggregations in a single statement. This clause is used to compute aggregations based on multiple grouping sets. ROLLUP is a shorthand for GROUPING SETS. For example, GROUP BY warehouse, product WITH ROLLUP is equivalent to GROUP BY GROUPING SETS ((warehouse, product), (warehouse), ()). The N elements of a ROLLUP specification results in N+1 GROUPING SETS.
CUBE: CUBE clause is used to perform aggregations based on combination of grouping columns specified in the GROUP BY clause. CUBE is a shorthand for GROUPING SETS. For example, GROUP BY warehouse, product WITH CUBE is equivalent to GROUP BY GROUPING SETS ((warehouse, product), (warehouse), (product), ()). The N elements of a CUBE specification results in 2^N GROUPING SETS.
aggregate_name: Specifies an aggregate function name (MIN, MAX, COUNT, SUM, AVG, etc.).
DISTINCT: Removes duplicates in input rows before they are passed to aggregate functions.
FILTER: Filters the input rows for which the boolean_expression in the WHERE clause evaluates to true are passed to the aggregate function; other rows are discarded.

Examples

{% highlight sql %} CREATE TABLE dealer (id INT, city STRING, car_model STRING, quantity INT); INSERT INTO dealer VALUES (100, 'Fremont', 'Honda Civic', 10), (100, 'Fremont', 'Honda Accord', 15), (100, 'Fremont', 'Honda CRV', 7), (200, 'Dublin', 'Honda Civic', 20), (200, 'Dublin', 'Honda Accord', 10), (200, 'Dublin', 'Honda CRV', 3), (300, 'San Jose', 'Honda Civic', 5), (300, 'San Jose', 'Honda Accord', 8);

-- Sum of quantity per dealership. Group by id. SELECT id, sum(quantity) FROM dealer GROUP BY id ORDER BY id; +---+-------------+ | id|sum(quantity)| +---+-------------+ |100| 32| |200| 33| |300| 13| +---+-------------+

-- Use column position in GROUP by clause. SELECT id, sum(quantity) FROM dealer GROUP BY 1 ORDER BY 1; +---+-------------+ | id|sum(quantity)| +---+-------------+ |100| 32| |200| 33| |300| 13| +---+-------------+

-- Multiple aggregations. -- 1. Sum of quantity per dealership. -- 2. Max quantity per dealership. SELECT id, sum(quantity) AS sum, max(quantity) AS max FROM dealer GROUP BY id ORDER BY id; +---+---+---+ | id|sum|max| +---+---+---+ |100| 32| 15| |200| 33| 20| |300| 13| 8| +---+---+---+

-- Count the number of distinct dealer cities per car_model. SELECT car_model, count(DISTINCT city) AS count FROM dealer GROUP BY car_model; +------------+-----+ | car_model|count| +------------+-----+ | Honda Civic| 3| | Honda CRV| 2| |Honda Accord| 3| +------------+-----+

-- Sum of only 'Honda Civic' and 'Honda CRV' quantities per dealership. SELECT id, sum(quantity) FILTER ( WHERE car_model IN ('Honda Civic', 'Honda CRV') ) AS sum(quantity) FROM dealer GROUP BY id ORDER BY id; +---+-------------+ | id|sum(quantity)| +---+-------------+ |100| 17| |200| 23| |300| 5| +---+-------------+

-- Group by processing with CUBE clause. -- Equivalent GROUP BY GROUPING SETS ((city, car_model), (city), (car_model), ()) SELECT city, car_model, sum(quantity) AS sum FROM dealer GROUP BY city, car_model WITH CUBE ORDER BY city, car_model; +--------+------------+---+ | city| car_model|sum| +--------+------------+---+ | null| null| 78| | null| HondaAccord| 33| | null| HondaCRV| 10| | null| HondaCivic| 35| | Dublin| null| 33| | Dublin| HondaAccord| 10| | Dublin| HondaCRV| 3| | Dublin| HondaCivic| 20| | Fremont| null| 32| | Fremont| HondaAccord| 15| | Fremont| HondaCRV| 7| | Fremont| HondaCivic| 10| | SanJose| null| 13| | SanJose| HondaAccord| 8| | SanJose| HondaCivic| 5| +--------+------------+---+ {% endhighlight %}

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Description

Syntax

Parameters

Examples

Related Statements

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