### 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>
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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 ofGROUP BY warehouse
andGROUP BY product
. This clause is a shorthand for aUNION ALL
where each leg of theUNION ALL
operator performs aggregation of subset of the columns specified in theGROUPING 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 forGROUPING SETS
. For example,GROUP BY warehouse, product WITH ROLLUP
is equivalent toGROUP BY GROUPING SETS ((warehouse, product), (warehouse), ())
. The N elements of aROLLUP
specification results in N+1GROUPING SETS
. CUBE
-
CUBE
clause is used to perform aggregations based on combination of grouping columns specified in theGROUP BY
clause.CUBE
is a shorthand forGROUPING SETS
. For example,GROUP BY warehouse, product WITH CUBE
is equivalent toGROUP BY GROUPING SETS ((warehouse, product), (warehouse), (product), ())
. The N elements of aCUBE
specification results in 2^NGROUPING 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 theWHERE
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|
+---+-------------+
-- Aggregations using multiple sets of grouping columns in a single statement. -- Following performs aggregations based on four sets of grouping columns. -- 1. city, car_model -- 2. city -- 3. car_model -- 4. Empty grouping set. Returns quantities for all city and car models. SELECT city, car_model, sum(quantity) AS sum FROM dealer GROUP BY GROUPING SETS ((city, car_model), (city), (car_model), ()) ORDER BY city; +--------+------------+---+ | 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| +--------+------------+---+
-- Alternate syntax for GROUPING SETS
in which both GROUP BY
and GROUPING SETS
-- specifications are present.
SELECT city, car_model, sum(quantity) AS sum FROM dealer
GROUP BY city, car_model GROUPING SETS ((city, car_model), (city), (car_model), ())
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|
+--------+------------+---+
-- Group by processing with ROLLUP
clause.
-- Equivalent GROUP BY GROUPING SETS ((city, car_model), (city), ())
SELECT city, car_model, sum(quantity) AS sum FROM dealer
GROUP BY city, car_model WITH ROLLUP
ORDER BY city, car_model;
+--------+------------+---+
| city| car_model|sum|
+--------+------------+---+
| null| null| 78|
| 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|
+--------+------------+---+
-- 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 %}